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TUFTS UNIVERSITY LIBRARIES
3 9090 014 531 558
Webster Family Library of Veterinary Medicine
Cummings School of Veterinary Medicine at
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200 Westboro Road
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fIDofcern Science Series
EDITED BY SIR JOHN LUBBOCK, BART., M. P.
THE HORSE
MODERN SCIENCE SERIES.
Edited by Sir JOHN LUBBOCK, Bart., M.P.
I. The Cause of an Ice Age.
By Sir Robert Ball, LL. D., F. R. S.
II. The Horse:
A Study in Natural History.
By William Henry Flower, C. B ,
Director of the British Natural
History Museum.
In press:
III. The Oak:
A Popular Introduction to Forest
Botany.
By H. Marshall Ward, F. R. S.
IV. The Laws and Properties of Mat-
ter.
By R. T. Glazebkook, F. R. S., Fellow
of Trinity College, Cambridge.
New York : D. Appletox & Co., 1, 3, & 5 Bond St.
g
6f
es •"
a
o
O
THE HOESE
A STUDY IN NATURAL HISTORY
BY
WILLIAM HENRY FLOWER, C. B.
LL. D., D. C. L., Sc. D., F. R. S., Pres. Z. S., Etc.
DIRECTOR OF THE BRITI8H NATURAL HISTORY MUSEUM
FORMERLY HUNTEIUAN PROFtSSOR OF COMPARATIVE ANATOMY ANI> PHY8IOLOGY
AT THE ROYAL COLLEGE OF SURGEONS OF ENGLAND
AND SOMETIME EXAMINER IN ANATOMY
AT THE ROYAL COLLEGE OF VETERINARY SURGEONS
NEW YORK
D. APPLETON AND COMPANY
1892
2.
COPTKIGIIT. 1891,
Bt d. applkton and company
All rights reserved.
DEDICATED
TO THE MEMORY OF MY FATHER
EDWARD FORDHAM FLOWER
(b. 1805, d. 1883)
WHO DEVOTED A GREAT PART OF HIS LIFE TO THE ENDEAVOUR
TO ALLEVIATE THE SUFFERINGS INFLICTED BY MAN
UPON THE HORSE
EDITOR'S INTRODUCTION.
The works to be comprised in this Series are in-
tended to give on each subject the information which an
intelligent layman might wish to possess. They are not
primarily intended for the young, nor for the specialist,
though even to him they will doubtless be often useful
in supplying references, or suggesting lines of research.
Each book will be complete in itself, care, however,
being taken that while the books do not overlap, they
supplement each other ; and while scientific in treat-
ment, they will be, as far as possible, presented in
simple language, divested of needless technicalities.
The rapid progress of science has made it more and
more difficult, and renders it now quite impossible, to
master the works which appear, almost daily, on various
branches of science, or to keep up with the proceedings
of our numerous Scientific Societies.
A distinguished statesman has recently expressed
the opinion, that we cannot expect in the next fifty
years any advance in science at all comparable to that of
the last half-century. Without wishing to dogmatise, I
viii EDITOR'S INTRODUCTION.
should be disj:>osed to hope that in the future the prog-
ress of science will be even more rapid.
In the first place, the number of students is far
greater; in the second, our means of research — the
microscope and telescope, the spectroscope, photography,
and many other ingenious appliances — are being added
to and rendered more effective year by year ; and, above
all, the circle of science is ever widening, so that the
farther we advance the more numerous are the problems
opening out before us.
No doubt there are other Scientific Series, but it is
not believed that the present will exactly compete with
any of them. The International Scientific Series and
Nature Series are no doubt useful and excellent, and
some of the volumes contained in them would well
carry out the ideas of the Publishers, but, as a rule, they
are somewhat more technical and go into minuter de-
tails.
The names of the Authors are a sufficient guarantee
that the subjects will be treated in an interesting and
thoroughly scientific manner.
High Elms, Farnborough :
November, 1891.
P K E F A C E
According to Iiuth's valuable " Bibliographical
Record of Hippology" (Works on Horses and
Equitation), published in the year 1887, there had
been up to that date at least 3,800 separate works
published in the various languages of the civilised
world on subjects appertaining to the horse. This
enumeration is, of course, far from perfect, and
very many additions are being made yearly to the
list.
I confess that I should have felt some hesitation
at adding another to this formidable array if I did
not believe that the subject has never been ap-
proached from the standpoint of this little work,
and that therefore something will be found in it
which is not to be met with in, any of those hitherto
written. In fact, it is only the knowledge which
has in very recent times accumulated from various
sources which could have made such a work pos-
sible.
x PREFACE
It endeavours to look at the horse as the animal
appears in the light of the modern and now gener-
ally accepted doctrines of Natural History, and in
thus doing it may be the means of teaching what
some of those doctrines are, and so of affording
insight into the methods of nature applicable to a
far wider range of study and of thought than that
limited to any single species.
By permission of the publishers of the " Ency-
clopaedia Britannica " some passages from my arti-
cles on the Horse and allied animals which ap-
peared in the ninth edition of that work have been
incorporated in this memoir, and I am greatly in-
debted to Mr. Gambier Bolton, Major J. Fortune
Nott, and Mr. York, for the use of the original
photographs from which the figures of the tapir,
rhinoceros, and various members of the horse fam-
ily have been reproduced. That of the quagga is
especially interesting, as being from the only photo-
graph known to have been taken of this animal in
a living state.
W. H. F.
May, 1S91.
CONTEXTS
CHAPTER I.
PAGE
The Horse's Place in Nature — Its Ancestors and
Relations 1
Interest of the study of the horse, especially as illustrat-
ing some important principles in biology — A test case of
the value of the theory of transmutation of species — Sig-
nificance of rudimentary structures — Meaning of the term
"specialization" — Position of the horse in the animal king-
dom— Division of ungulate mammals into perissodactyle and
artiodactyle — The horse belongs to the former — Palasonto-
logical history of the perissodactyles — Generalized ungulates
of the earliest Eocene age — Phenacodus — True perissodac-
tyles— Hyracotherium — Palaeotherium — Families which be-
came extinct without leaving descendants — Three surviv-
ing families, represented at the present time by the Ta-
pirs, Rhinoceroses, and Horses— The first the least and the
last the most modified — Principal characters by which
horses differ from the generalized early forms of perissodac-
tyles, probably all adaptations to changed conditions of life
— Present state and probable future of the group.
CHAPTER II.
The Horse and its Nearest Existing Relations . . 45
The tapirs (Family Tapiridce) — Characters, species, geo-
graphical and geological distribution— The rhinoceroses
(Family Rhinocerotidw)— The horses (Family Eqmdw)—
Their immediate predecessors — The hipparions, or three-
xji CONTENTS.
PAGE
toed horses of Europe and America — Existing species of
horses — The horse {Equus caballus) — Wild, domesticated,
and feral horses — Wild assss — Equus hemiouus of Asia and
its varieties — The African wild ass and the domestic ass
{Equus asinvs) — Striped members of the equine family —
Zebras and quaggas {Equus ztbra, E. burchelU, E. cjrevyi,
and E. quagga) — Hybrids or mules — Aptitude for domesti-
cation only found in certain members of the family.
CHAPTER III.
The Structure of the Horse, chiefly as bearing upon
its Mode of Life, its Evolution, and its Relation
to other Animal Forms 102
The skull — The teeth : their number ; general characters
and structure ; crown, root, pulp, dentine, enamel, and ce-
ment— Succession of teeth — Temporary and permanent sets
— Special characters of the teeth of the horse — Incisors —
( anines — Diastema — Molars — Brachydont and hypsodont
dentition— Temporary or milk teeth— Time of appearance
and order of succession of the teeth— The lips— The nostrils
—The false nostrils— The guttural pouches— The neck —
Vertebrae— Cervical ligament.
CHAPTER IV.
TnE Structure of the Horse— (continued) . . .153
General characters of the limbs of vertebrated animals-
Comparison of the skeleton of the fore limb of the horse with
that of man— Comparison of the skeleton of the hind limb
of the horse with that of man— The muscles of the limbs—
The warts or callosities on the external surface of the limbs
The ergot or spur — The chestnuts, or mallenders and sal-
lenders— The hoofs.
ILLUSTRATIONS
FIG. PAGE
Comparative view of skeletons of man and horse
(Frontispiece)
1. Diagrammatic representation of skeletons of the fore
foot of perissoclactyle and artiodactyle ungulates . 15
2. Restoration of the skeleton of Phenacodus primcevus . 21
3. Upper molar teeth of Phenacodus, Ilyracotherium, and
Anchitherium 31
4. Bones of the foot of Anchitherium .... 37
5. Bones of the foot of Hipparion 38
6. Bones of the foot of horse 39
7. Plantar surface of fore and hind foot of Malay tapir . 47
8. American tapir (Tapirus americanus) .... 50
9. Indian rhinoceros (Rhinoceros unicornis) ... 61
10. Section of molar tooth of Hipparion .... 71
11. African wild ass (Equus asinus) and foal ... 87
12. Common or mountain zebra (Equus zebra) ... 91
13. Burchell's zebra (Equus burchelli) .... 93
14. Quagga (Equus quagga) 96
15. Side view of skull of man . . - . . . . 107
16. Side view of skull of horse 109
17. Incisor tooth of Anchitherium aurelianense . . . 121
18. Unworn crown of temporary incisor tooth of young
horse 121
1
xiv ILLUSTRATIONS
FIG. • PAGE
19. Incisor tooth of horse with the crown partially worn . 122
20. Side view of brachydont and hypsodont molars of An-
chitherium and horse 131
21. Grinding-surface of molar teeth of Anchitherium and
horse 133
22. Cervical ligament, and bones to which it is attached, of
horse 149
23. Plantar surface of the foot of man, dog, and horse . 179
24. Section of the finger of man 190
25. Section of the foot of horse 191
26. Under surface of hoof of horse 199
THE HORSE.
CHAPTER I.
THE HORSE'S PLACE IN NATURE — ITS ANCESTORS AND
RELATIONS.
Interest of the study of the horse, especially as illustrating
some important principles in biology — A test case of the
value of the theory of transmutation of species — Signifi-
cance of rudimentary structures — Meaning of the term
" specialization" — Position of the horse in the animal king-
dom— Division of ungulate mammals into perissodactyle
and artiodactyle — The horse belongs to the former — Pa-
lseontological history of the perissodactvles — Generalized
ungulates of the earliest Eocene age — Phenacodus — True
perissodactyles — Hyracotherium — Pala?otherium — Fami-
lies which became extinct without leaving descendants —
Three surviving families, represented at the present time
by the Tapirs, Rhinoceroses, and Horses — The first the
least and the last the most modified — Principal charac-
ters by which horses differ from the generalized early
forms of perissodactyles, probably all adaptations to
changed conditions of life — Present state and probable
future of the group.
The horse is from many points of view one of
the most interesting of animals. In utility to man it
yields to no other. It was his domestic companion,
2 THE HOKSE.
friend, and servant before the dawn of history. It
has accompanied him in his wanderings over almost
every part of the surface of the earth, performing
duties both in peace and war which no other animal
could have done, and giving Man facilities for the
exercise of dominion over nature which otherwise
would have been impossible to him. The role of the
ass, the ox, the camel, and the llama in performing
similar duties has been of a limited and subsidiary
nature compared to that of the horse.
It is only in very recent times that the progress
of mechanical invention has begun to supersede
some of the uses for which the strength and the
speed of the horse for many thousands of years have
alone been available. How far this commencing dis-
establishment of the horse from its unique position
as the main agent by which man and his posses-
sions have been carried and drawn all over the face
of the earth will go, it is difficult to say at present-
To the eye of the naturalist, the horse presents
other and still higher sources of interest. No better
example can be found in the whole range of the ani-
mal kingdom to illustrate certain great principles
found acting universally in the construction of the
bodies of all living beings, whether animals or plants.
The structure of the horse in relation to that of allied
animals and to the actions which it has to perform
ITS PLACE IN NATURE. 3
ill the economy of nature may be most advanta-
geously studied by every one who wishes to gain an
insight into some of the fundamental principles of
biology. In scarcely any other animal has specializa-
tion of various parts — that is, modification from the
general or average type to conform to the require-
ments of some special mode of existence — been car-
ried to such an extreme. In many organs, but espe-
cially in the limbs and teeth, we find the strongest
evidence of two opposing principles striving against
each other for the mastery in fashioning their form
and structure. We find heredity, or adherence to a
general type derived from ancestors, opposed by spe-
cial modifications of or deviations from that type, and
the latter generally getting the victory, although in
the numerous rudimentary structures that remain
there is significant evidence of ancestral conditions
long passed away. The various specializations, evi-
dently in adaptation to purpose, will be thought by
many to be the result of the survival, in the severe
struggle for existence, of what is best fitted for the
purpose to which it is to be applied. This may or
may not be the explanation, but the interest of the
study of such an animal as the horse will be in-
creased tenfold by the conviction that there is some
true and probably discoverable causation for all its
modifications of structure, however far we may yet
4 THE HOUSE.
be from the true solution of the methods by which
they have been brought about.
The anatomy and history of the horse are, more-
over, often taken as affording a test case of the value
of the theory of evolution, or, at all events, of the
doctrine that animal forms have been transmuted or
modified one from another with the advance of time,
whether, as extreme evolutionists hold, by a sponta-
neous or inherent evolving or unrolling process, or,
as many others are disposed to think, by some mys-
terious and supernatural guidance along certain defi-
nite lines of change. It will be observed that both
these views are opposed to the doctrine, formerly
held universally by naturalists and theologians alike,
that each modification of animal or plant form suffi-
ciently distinct to be called a species had a separate
origin — a doctrine for which, it may be remarked by
the way, no proof of any kind has ever been offered.
The evidence in favor of the theory of transmu-
tation afforded by the case of the horse is derived
from two distinct sources — (1) The structure of ex-
isting horses ; (2) the past history of the race as re-
vealed by fossil remains.
(1) By far the most interesting portions of the or-
ganization of existing horses from this point of view
are the various rudimentary and apparently useless
structures which occur in several parts of its body,
ITS PLACE IN NATUKE. 5
structures which correspond to some which are fully
developed and functional in other animals, but which,
in the horse, are so reduced in size or altered in
character as to be of little or not any use in its
economy.
Parts, usually called rudimentary, may be in one
of two conditions : either nascent, or in process of
growth to something larger and more useful ; or ves-
tigial— that is, in a dwindling and degenerate state,
vestiges of a once more developed condition. In any
particular case, it may be difficult to say to which
category it should be assigned, and we may have to
look for guidance beyond the mere structure itself.
In all or nearly all which we shall meet with in the
horse, the presence of the same parts in a fully de-
veloped state in other allied though less specialized
animals points clearly to the second condition, a con-
clusion which is strengthened by the certain knowl-
edge derived from palaeontology that the horse in its
present form has only come into existence at a very
late period of the world's history — is, in fact, one of
the most modern forms of animal known.
In tracing the history and affinities of animals,
rudimentary organs are looked upon by naturalists
as far more important than highly developed or
functional parts. As Darwin says, they "may be
compared with the letters of a word, still retained in
6 THE HORSE.
the spelling but become useless in the pronunciation,
but which serve as a clue for its derivation* On the
view of descent with modification we may conclude
that the existence of organs in a rudimentary, im-
perfect, or useless condition, or quite aborted, far
from presenting a strange difficulty, as they assur-
edly do on the old doctrine of creation, might even
have been anticipated in accordance with the views
here explained."
The rudimentary parts met with in the structure
of the horse will be described fully in the last two
chapters of this work, which treat of the anatomical
characters of the animal.
(2) It is, however, to the ancestral history, as
disclosed by palaeontology, or the study of fossil
remains, that we must look for the more direct evi-
dence of the truth of the theory ; and we are in a
better position to do this in the case of the horse
than in that perhaps of any other animal, as it is one
of the few whose history can be traced through a
tolerably complete chain of links as far back as the
earliest Tertiary age.f We must, however, not carry
* As, for example, the b in "debt" and "doubt."
t The latest of the three great periods into which geolo-
gists divide the age of the earth is called Tertiary or Caino-
zoic. It is subdivided into Eocene, Miocene, Pliocene, and
Pleistocene, the last being that which immediately preceded
the one in which we are now living.
ITS PLACE IN NATUKE. 7
away the idea that the record is yet perfect. Before
the commencement of the Eocene period it is wrapped
in what appears at present impenetrable darkness
and mystery.
Throughout the vast Tertiary period, fragments
here and fragments there stand out among the ruins,
from which we endeavor to reconstruct our edifice,
just as the skillful architect or antiquary, from the
shattered pieces of marble or stone of an ancient
temple, will restore to us the noble forms and pro-
portions it once bore.
The outcome of all recent work in this subject
has been, that every fresh discovery which has been
made has tended to corroborate, and nothing has
been found inconsistent with, the view that the liv-
ing beings which we see around us have been gradu-
ally fashioned into shape by the modification of
pre-existing forms — a view of creation which is the
grandest, most sublime, and at the same time most
reasonable, which has yet been presented to us.
A few words may be said here upon the impor-
tant subject of specialization, which will be so fre-
quently referred to in what follows. The modifica-
tions in animal structure which come under this defi-
nition may be grouped under three principal head-
ings : (1) The addition of parts not met with in the
generality of animals, and, as far as is known, not
8 THE HOESE.
found in the earliest members of the group which
afterwards possess them — as, for example, the antlers
of deer, the horns of oxen or the rhinoceros, the
humps of camels, etc. (2) The suppression of parts
commonly present — as the upper front teeth of rumi-
nants, the tails of bears and guinea-pigs, the outer
toes of the horse's foot, the entire hind limbs of por-
poises, etc. (3) The modification of the form, size,
and relation of parts — as the immense development
of the tusks in the walrus and male musk-deer, the
complicated foldings of the grinding teeth of ele-
phants, etc.
In tracing out any series of gradual modifications
following each other in a regular chronological se-
quence, as we are sometimes fortunate enough to be
able to do,* we find that progress is usually from the
general to the special. It must not, however, be sup-
posed from this statement that all animals living
in ancient times were more generalized in character
than many now existing. On the contrary, many
of the extinct forms, even those of quite early
periods, were in some portion of their structure
very highly specialized. In fact, high specialization
almost invariably leads ultimately to extinction, be-
* Many such instances are described in an interesting se-
ries of works, entitled Les Encliainements du Monde Animal
dans les Temps Geologiques, by Professor Albert Gaudry,
Paris, 1878-90.
ITS PLACE IN NATURE. 9
cause it results from adaptation to particular con-
ditions, which may become changed in course of
tirue, and then the animals which have become
adapted exclusively for life, under those conditions
perish, while those animals that retain more general
characters readily adapt themselves to the altered
circumstances. The commonplace, average sort of
creatures are thus often the longest lived as species,
while such very strangely modified forms as TJinta-
therium* 3Iachair otitis, \ and Tlujlacoleo,% passed rap-
idly over the stage and then vanished from sight.
It is proposed in this little work to treat of the
horse, not as an isolated form, but as one link in a
great chain, one term in a vast series, one twig of a
mighty tree ; and to endeavor to trace, as far as our
present knowledge permits, what its relations are to
the rest, and by what steps of modification in its
* A huge beast from the Eocene of North America, with
limbs resembling those of an elephant, and a rhinoceros-like
skull, but with great descending flattened tusks in the upper
jaw, and three pairs of bony prominences, like horns, on the
top of the head.
t An animal allied to the tiger, with enormous saber-like
upper canines, found in the later Tertiaries of both Europe
and America.
X A marsupial of the late Tertiary period of Australia, as
large as a sheep, allied to the phalangers and kangaroos, but
with one huge cutting cheek-tooth (premolar), and one great
incisor on each side of each jaw, all the other teeth being ex-
tremely reduced in size and almost functionless.
10 THE HOUSE.
various parts it has come to be the very singular and
highly specialized animal we have now before us, so
distinct from all existing forms of life that in most
of the older zoological systems it was (at least asso-
ciated only with some very immediate allies, struc-
turally almost identical) placed in an order apart
from all other mammals, under the name of Solid-
ungula, Solipedia, or Monodactyla, the animal with
the solid foot, or rather with a single toe on .each ex-
tremity.
As will be seen from the sequel, the various
forms of asses and zebras only differ from the horse
in slight details of their organization, and with it
form a group entirely apart from all other existing
animals, a group constituting the genus Equus and
the family Uquidce, but no longer considered so
isolated as to form a distinct order. In much of
what follows the term " Horse," unless the contrary
is especially stated, must be understood to include
the other members of the family.
To understand the natural place of the horse in
the zoological system it will be necessary to take
a wide glance at the whole great group to which
it belongs. That it is a vertebrate animal, and
that it occupies a place in the class Mammalia,
no one will doubt. Within that class there can also
be no doubt about its taking its place in the great
ITS PLACE IN NATUEE. 11
division of Eutheria, which includes all existing
mammals except the Marsupials and Monotremes.
In treating only of existing mammals, a division
of the class into distinctly circumscribed groups is
perfectly easy. The so-called orders generally ac-
cepted are separated from each other by well-
marked breaks of continuity. Many extinct forms
can also be contained within the definitions of these
orders. But the rapid advance of palaeontology is
disclosing to view an enormous number of long-
buried animal forms, which are gradually filling up
all the spaces left between the isolated groups now
surviving on the earth, and continually increasing
the difficulty of giving satisfactory definitions of
their boundaries.
In the first serious attempt at the classification of
the Mammalia, that of John Ray, in his "Synopsis
Methodica Animahum," published in 1693, the class
was separated into two great divisions, the ungulated
or hoofed animals, and the unguiculated, or those
with nails or claws. This division, especially as
applied by its author, was somewhat artificial, the
camel being separated from all its ungulate allies, and
placed in the unguiculate division, and the latter
embracing a very heterogeneous assemblage of crea-
tures. Nevertheless, some portion of this system
has survived, and especially the group JJnguJata, dis-
12 THE HORSE.
carded by Linnseus, Cuvier, and others, and broken
np by them in several distinct orders, has been resus-
citated of late years, and is now generally used, with
almost the same limits as were assigned to it by Ray.
The Ungulata in this sense are all animals emi-
nently adapted for a terrestrial life, and in the main
for a vegetable diet. Though a few are more or less
omnivorous, and may under some circumstances
kill living creatures smaller and weaker than them-
selves for food,* none are distinctly and habitually
predaceous. Their molar or cheek-teeth have broad
crowns, with tuberculated or ridged grinding surf aces,
and they have a very completely developed set of milk-
teeth, which are not changed until the animals have
nearly attained maturity. Their limbs are adapted
for carrying the body in ordinary terrestrial progres-
sion, and are of very little use for any other purpose,
such as flying, climbing, seizing prey, or carrying
food to the mouth. They have no clavicles or collar-
bones. Their toes are provided with blunt, broad
nails, winch in the majority of cases more or less
surround and inclose their ends, and are called
hoofs. Leaving aside certain forms which are not
so nearly related to the subject of this memoir as to
concern us further and which are nearly all extinct,
the majority of the ungulated animals have been
* Pigs, for instance, will kill and eat snakes.
ITS ANCESTORS AND RELATIONS. 13
throughout the whole of the Tertiary period sepa-
rated into two perfectly distinct sections, differing
from each other not only in the obvious characters
of the structure of their limbs, but in numerous im-
portant points in other portions of their organi-
zation, such as their skull, vertebral column, teeth,
digestive organs, etc. The characters of these two
groups, first indicated by Cuvier, were thoroughly
established by Owen, by whom the names by which
they are now generally known were proposed. These
are Artiodactyla, or even-toed, and Perissodactyla, or
odd-toed*
It is only by studying the fundamental type of
organization common to all members of a group
which underlies the various external or superficial
modifications by which it becomes adapted to the
different surrounding conditions under which it has
to carry on its existence, that the true relationship of
animals can be determined. In this way it can be
clearly demonstrated that the pig, the deer, the ox,
sheep, goat, antelope, and camel, including even such
extreme forms as the giraffe and the hippopotamus,
are formed on one plan — the Artiodactyle ; while the
horse, the tapir, and the rhinoceros are formed on
the other — the Perissodactyle type.
* From the Greek artios, even in number, and perissos, un-
even ; combined with daktylos, finger or toe.
14 THE HOESE.
To understand one of the principal distinctions
between these two forms, it must be premised by
way of explanation that the number of digits (a con-
venient common term to express either fingers or
toes, whether of the fore or hind foot) in mammals
never exceeds five on each limb. For convenience
of description, they are designated numerically from
the inner side of the limb — L, II., III., IV. and V.
(Fig. 1, p. 15) the pollex (thumb) and hallux (great toe)
being the first of the fore and hind limbs respect-
ively, and the third is the middle of the complete
series. When the number falls short of five, it is
always easy to determine, by their relations to the
bones of the wrist or ankle, which of the typical
series are present and which are missing.
In the Artiodactyles the third and fourth digits
of both feet are almost equally developed, and flat-
tened on their inner or contiguous surfaces, so that
each is not symmetrical in itself, but when the two
are placed together they form a figure symmetrically
disposed to a line drawn between them, and consti-
tute the erroneously called " cloven hoof " of the Ru-
minants, which is really not one, but the two hoofs
of distinct toes. These two digits are always pres-
ent and well developed ; the second and fifth may
be present in varying degrees of development, or
may be entirely absent; the first is not present in
ITS ANCESTOKS AND KELATIONS.
15
any known member of the group, even the most
ancient.
Fig. i, — a, diagrammatic representation of the bones
of the right fore-foot of an odd-toed or Perissodac-
tyle animal. B, of an even-toed or Artiodactyle.
C, the carpus or wrist, consisting of two rows of
bones, the upper being c, cuneiform ; 7, lunar ; and
s, scaphoid ; the lower, u, unciform ; m, magnum ;
td, trapezoid, and tm, trapezium- The long bones
in contact with the last constitute the metacarpus ;
the remaining bones are the phalanges. The digits
or toes are numbered in order from the inner to the
outer side of the foot. The shaded parts of A are
those that are present in the horse ; in B, those that
are present in the ox.
16 THE HORSE.
In the Perissodactyle group, the middle or third
digit of both fore and hind feet is larger than any of
the others, and symmetrical in itself, the free border
of the last bone (the ungual phalanx, which supports
the hoof *) being evenly rounded on both sides. This
may be the only digit sufficiently large to be of any
use to the animal, as in the horse, or the second and
f oui'th may be nearly equally developed on each side
of it, as in the rhinoceros. In the tapir and in many
extinct forms, the fifth digit is also present in the
fore foot j but this does not interfere with the sym-
metrical arrangement of the rest of the foot around
the median line of the third or middle digit. A first
digit (pollex or hallux) has only been found in some
extremely ancient and primitive forms.
It will not be necessary to enter into any descrip-
tion of the remaining anatomical characters by which
these two groups are distinguished, although, as be-
fore said, they are very marked, and pervade almost
every portion of their organization. The differen-
* The phalanges are the separate bones of which the dig-
its are composed. They are three in number in each digit,
called respectively first, second, and third, or proximal, mid-
dle, and distal ; the last being often also called "ungual," be-
cause it supports the nail or hoof. The metacarpals and
metatarsals are the long bones which connect the carpus
(wrist-bones) or tarsus (ankle-bones) with the digits in the
fore and hind limb respectively. When a word common for
both is required, they are spoken of as "metapodials."
ITS ANCESTORS AND RELATIONS. 17
tial characters of the feet can be readily appreciated,
even by those who have little anatomical knowledge,
and suffice to show the fundamental distinction be-
tween them.
Having now eliminated from consideration all
mammals but ungulates, and all ungulates but peris-
sodactyles, we may henceforth confine our attention
solely to this group, as it is the one which contains
the horse and all its nearest relatives, and we must
first endeavor to trace its history back in geological
time as far as our available records will take us.
It is now well known that mammals existed far
back into the secondary or mesozoic age, as far back
as the Khaetic or uppermost beds of the Triassic
system j but these had none of the characters of
ungulates. They were all very small in size, and
apparently more nearly allied to the Mar supi alia
and Insectivora than to any other existing orders.
Until quite recently not a trace of any mammal had
been found in any of the strata attributed to the great
Cretaceous epoch. The blank has, however, been
partially filled up by the discoveries in North Amer-
ica announced by Professor Marsh ; but we know
as yet too little of these to be able to form any satis-
factory opinion as to their affinities, or to pronounce
with any certainty whether they carry back the pedi-
gree of the perissodactyle group beyond the com-
18 THE HORSE.
mencement of the Tertiary period. At present the
balance of evidence is rather in favor of their rela-
tionship with, the earlier and more primitive forms
jnst mentioned. We have, however, certain knowl-
edge that when the land which formed the bottom
of the great cretaceous ocean which flowed over a
considerable part of the present continents of Europe
and North America was lifted above the level of the
water and became fitted to be the abode of terrestrial
animals, it was very soon the habitation of vast num-
bers of herbivorous and hoofed mammals.
The remains of animals to which it is possible to
trace back the modern horse by a series of successive
modifications without any great break are found in
abundance in the lower strata of the great lacustrine
formations assigned to the Eocene period spread over
considerable portions of the present territories of
New Mexico, Wyoming, and Utah, in North America.
Similar animals also existed in other parts of the
world, but in Europe the hitherto-discovered frag-
ments which prove their existence are in a less com-
plete and satisfactory condition for investigation.
Negative evidence is in such cases, however, of little
value, as may be judged from the fact that it is only
within a very few years that the existence of these
American deposits teeming with fossil remains of
previously unsuspected forms of lif e has been brought
ITS ANCESTOKS AND KELATIONS. 19
to light. How do we not know that the next ten or
twenty years may not be equally fruitful in new dis-
covery ?
After giving a summary of what was then known
of the ancestry of the horse, as disclosed by palgeon-
tological evidence, Professor Huxley wrote in 1877 :#
" The knowledge we now possess justifies us com-
pletely in the anticipation that when the still lower
Eocene deposits and those which belong to the cre-
taceous epoch have yielded up their remains of an-
cestral equine animals, we shall find, first, a form
with four complete toes and a rudiment of the in-
nermost or first digit in front, with probably a rudi-
ment of the fifth digit in the hind foot j while in still
older forms, the series of the digits will be more and
more complete, until we come to the five-toed ani-
mals, in which, if the doctrine of evolution is well
founded, the whole series must have taken origin."
This anticipation has been completely verified by
the discovery, among others, of PJienacodus in the
Wasatch beds, which there is every reason to believe
are nearly, if not quite, the oldest of the Eocene for-
mations of North America.
Although this most interesting animal was known
and named by Cope as long ago as 1873 from teeth
alone, it was not until the more recent discov-
* American Addresses : Lectures on Evolution, p. 89.
20 THE HOESE.
eries by Wortman of complete skeletons of more
than one individual with all their bones in connec-
tion that we were put in possession of almost as per-
fect a knowledge of its osteological characters as of
any animal now existing. The figures and descrip-
tions published by Professor Cope,* and the excel-
lent casts sent to this country of one of the skeletons,
have made this knowledge widely accessible. Al-
though this creature was of an extremely generalized
form, it was obviously so far separated from the
primitive mammalian type, whatever that may have
been, as to come within the definition of the ungu-
late group, using this term in its widest sense. The
terminal bones of the toes were of such a form as to
show that they were incased in hoofs, instead of car-
rying claws, and it had no clavicles. The teeth also
were adapted for a herbivorous or omnivorous diet.
Phenacodus, however, does not stand alone, even
in our present state of knowledge ; it belongs to a
family of which several generic modifications are
already described, and remains of still more general-
ized forms, the Periptychidce of Cope, are found in
the Puerco Eocene beds of New Mexico, probably
still older than the Wasatch. Forms apparently
allied have also been discovered by Rutimeyer in
* Report of the United States Survey of the Territories, vol.
iii. 1884.
ITS ANCESTORS AND RELATIONS.
21
22 THE HOUSE.
early Eocene formations in Switzerland. None of
these have been found in such a complete state as
Phenacodns ; it is scarcely necessary therefore to
dwell upon them here, though it will be well to de-
vote a little time to the consideration of the structure
of this form, which, if not in the actual ancestral
line of all ungulates (and also, according to Cope, of
the insectivores, carnivores, lemurs, monkeys, and
even Man himself !) at all events exhibits the primi-
tive pattern upon which the skeletons aud teeth of
all the others have been constructed, and which has
never been departed from in any of them, however
disguised by the special modifications of particular
parts.
No part of the organization of an animal is so
important in judging of its general position and
characters, and at the same time so perishable, as
the brain, and yet in consequence of this organ in all
the higher vertebrates being accurately adapted in
size and form to the bony case which contains it, we
have been able to obtain a wonderfully perfect
knowledge of, at all events, the rough anatomy of
the brain in many animals which ceased to exist
ages ago. A cast of the interior of the skull of Phe-
nacodus, made and figured by Cope, shows a remark-
ably low type, both as to size and form, as compared
with any modern ungulate of corresponding dimen-
ITS ANCESTORS AND RELATIONS. 23
sions. The hemispheres of the cerebrum are espe-
cially small, compared with the cerebellum aud ol-
factory lobes. This is exactly iu accord with what is
now generally known of the progressive diminution
of the size of the brain in all groups of animals the
further back we pass from the present time.
The teeth were of the same number as in the
great majority of Eocene mammals — namely, three
incisor or front teeth, one canine or corner tooth,
and seven cheek teeth, consisting of four premolars
and three molars,* or eleven altogether on each side
of the upper, and the same number in the lower, jaw,
making a total of forty-four. These numbers are
briefly expressed in the formula
. 3 1 4 3 11 _ AA
i-^c, jil»4>w3 = jj x 2 = 44.
This is an extremely important formula to. remem-
ber, as it is, as just mentioned, the one most com-
monly met with in mammals of the early Tertiary
periods, and therefore the most generalized condition
of dentition among all the higher orders of the class,
and the one from which, by suppression or loss of
certain of the teeth, all the special modifications now
* The back teeth, grinding teeth, or cheek teeth are di-
vided into premolars and molars or true molars. In the ungu-
lates there are three or four of the former and always three
of the latter, which are the hindermost of the series and not
preceded by milk teeth.
3
24 THE HORSE.
met with have been derived .* The characters of the
teeth, as well as their number, are of a generalized
type. The incisors are small, subequal, and with cut-
ting edges, and are set in a semicircular line. The
canines are, however, distinctly differentiated from
the other teeth, isolated from the incisors in front
and from the premolars behind, and are moderately
strong, conical, and pointed. The premolars and
molars are in a contiguous series, and the former are
distinctly denned from the latter by their simpler
structure. Their crowns are all extremely brachy-
dont, or short from above downwards, a character
met with in all primitive forms. The true molars
belong to the simplest, or " bunodont " t type, having
four principal rounded cusps on the grinding surface
of each, with smaller cusps between, making six al-
together. (See Fig. 3, A, page 31.)
The head is of small size compared with the body
generally. The orbits, or cavities for the eyes, are
not completed by bone behind, but are widely con-
tinuous with the temporal fossae on the side of
the skull, as in. all primitive forms. The vertebral
* In the pig and a few inseetivora alone among existing
mammals is this number retained. In all others the total
number of teeth falls short of forty-four, although, as we
shall see, some horses still retain (as an exceptional condi-
tion) the primitive formula.
t From the Greek bounos, a hill or mound.
ITS ANCESTOKS AND KELATIONS. 25
column is said to consist of seven cervical, fourteen
or fifteen thoracic, six or seven lumbar, and three to
five sacral vertebras. The tail is long and tapering,
much longer than in any existing ungulate, as it
must have reached quite to the ground in walking.
The scapula or shoulder-blade has a very oval form,
resembling that of a carnivore more than that of any
existing ungulate. The clavicles or collar-bones, as
previously mentioned, are lost*
* In using this expression the assumption is made that
Phenacodus, and, in fact, all other mammals, are derived
from forms having clavicles, and that the absence of these
bones is a case of specialization, an assumption supported by
the facts that the presence of clavicles is the rule in birds,
reptiles, and amphibia ; that they are well developed in vari-
ous orders of mammals not otherwise closely associated, as
marsupials, edentates, insectivores, and primates; and that
they are also found, though often in a more or less vestigial
condition, in rodents and carnivores. These facts all tend to
show, if they do not conclusively prove, that the presence of
the clavicle is the typical condition, notwithstanding its com-
plete absence in extensive groups of mammals, as the ungu-
lates and cetacea.
Since the above was in type the discovery has been an-
nounced of the presence of a rudimentary and transient clav-
icle in an early embryo of a sheep. This affords a complete
confirmation of the view above expressed, and is a most as-
tonishing instance of the persistence of a structure in the
embryonic condition, which has, as far as our evidence tells,
been absent in the adults during the whole of the Tertiary
period. H. Wincza, "Ueber ein transitorisches Eudiment
einer knochernen Clavicula bei Embryonen eines Ungulaten."
Morphol. Jahrbuch, xvi. p. 647. 1890.
26 THE HOUSE.
The humerus, or upper-arm bone, presents a
character not found in any of the existing ungulates,
although common in the caruivora — that of a perfora-
tion, or foramen above the inner condyle. The two
bones of the forearm, are, as in all generalized forms,
both fully developed, the ulna being of large size
throughout its length. The structure of the wrist,
or carpus, is of great interest from its extremely prim-
itive condition, each bone of the second row stand-
ing directly beneath, and articulating almost entirely
and only with, the corresponding bone of the first
row.
The five digits, with their typical number of pha-
langes, are completely developed, the third being the
longest and strongest. The terminal or ungual pha-
langes are expanded, flattened, and rather spatulate,
and evidently bore hoofs rather than claws. Each
digit has a metacarpal bone and three phalanges, ex-
cept the first or pollex (corresponding to the thumb
of man), which has but two.
In the hind leg, the femur or thigh-bone shows
considerable evidence of the presence of that project-
ing ridge on the outside, known as the third trochan-
ter, found in all Perissodactyles, but in none of the
Artiodactyle section. The two bones of the lower
leg, the tibia and fibula, are distinct and com-
plete.
ITS ANCESTORS AND RELATIONS. 27
In the ankle or tarsus the cuboid articulates with
the calcaneum only. The astragalus presents a uni-
formly convex distal articular surface, as in Carniv-
ora, but it has a trochlea or pulley-like proximal end,
which the still more generalized Periptychus has not.
The toes are five in number, much resembling those
of the fore-foot. The animal was apparently not
plantigrade, or walking with the whole of the sole of
the foot, from the heel or hock to the toes, on the
ground, as the bears do, nor did it walk on the tips
of the toes only, as the horse does, but probably ha-
bitually stood in an intermediate position, with the
heel raised more or less from the ground.
The remains of animals referable to this genus
already discovered in the Wasatch Eocene are re-
markably numerous, and differences in size and de-
tails of conformation have enabled Cope to describe
and name nine species considered to be distinct from
each other. They vary in size from that of a bull-
dog to a leopard or sheep. The structure of the bones
of the nasal region has led to the suggestion that the
head may have carried a short proboscis like that
of the tapir.
As mentioned above, Phenacodus is not an iso-
lated form, and allied but less perfectly known spe-
cies appear to bridge over the interval between it and
the next that will be spoken of.
28 THE HOUSE.
In the year 1839, Sir Richard Owen described an
imperfect skull of a small animal, not larger than a
fox, which was discovered in the London Clay (Lower
Eocene) of Heme Bay, in Kent, under the name of
HyracotJierium, a name implying a supposed affinity
(which we now know it does not possess) to the exist-
ing genus, Hyrax* Specimens of identical or similar
forms were subsequently found in Eocene formations
in England and other parts of Europe, and others re-
ferred to the same genus far more abundantly and in
a far more perfect state of preservation in beds of
corresponding age in North America. To a closely
allied form the name of Paeliynoloplius has been
given, while Plioloplius and OroMppus are probably
identical, and they are all so nearly related to a pre-
viously known but larger animal, called by Cuvier
Lophiodon, that they are commonly associated to
* " Hyrax " (a Greek word for an animal which cannot be
identified with certainty, perhaps a kind of shrew) is a name
given by modern zoologists to a small group, consisting of
about a dozen species, of animals inhabiting the rocky dis-
tricts of Syria and various parts of Africa, and which are of
such peculiar structure that they are completely separated
from all the existing and all the hitherto discovered extinct
forms of life. They form the order Hyracoidea of Huxley,
but may be included in the Ungulata, using that term in the
very widest sense. They are the animals whose Hebrew name
is translated in the English Bible into " coney " or rabbit, to
which in size, color, and habit they bear a considerable gen-
eral resemblance.
ITS ANCESTORS AND RELATIONS. 29
form a family Lophiodontidce. Some of these ani-
mals * present a very distinct advance in evolution
upon Phenacodus, an advance in some respects so
great as to move them, according to Cope, into a dis-
tinct ordinal division of the Mammalia. This con-
sists mainly in a modification of the form and re-
lations of the bones of the carpus and the tarsus
from their primitive condition, which modification
persists in all the more recent forms of true ungu-
lates, both Perissodactyle and Artiodactyle, and the
absence of which is the principal distinction between
them and the Proboscidea (elephants) and the Hyra-
coidea.
The bones of the second row of the carpus no
longer stand exactly below the corresponding bones
of the first row, but are all shifted a little way to
the inner side of the foot, a change which is facili-
tated by the disappearance of the first digit, and
which, with certain alterations in the form of the
articular surfaces, tends to produce a more perfect
interlocking of these bones one with another, and
* Madame Marie Pavlow has shown that under the name
of Hyracotherium some very different forms have been eon-
founded, the type species of Owen being the most primitive,
and perhaps identical with Cope's Phenacodus, while the Amer-
ican H. venticolum, of which the whole skeleton is known, and
to which the description in the text chiefly applies, is a much
more advanced form.
30 THE HOESE.
thereby greater stability to the carpal region as a
whole (see Fig. 1, p. 15). A corresponding change in
the tarsus brings the cuboid into articular relation
with the astragalus, which it wants in the primitive
condition.
In the number of the digits a considerable modi-
fication has taken place in both feet. In the fore-
limbs, instead of five, there are but four toes, a
number which was long retained by a considerable
section of the order, and persists even to the present
day in the one family of tapirs. A foot thus formed
may appear at first sight to belong to the Artiodac-
tyle or even-toed type, especially as the missing toe
is the first, and the four that remain are exactly
those of the Artiodactyles. But on examining a
little more closely it will be seen to present all the
structural characteristics of the five-toed Perisso-
dactyles, only changed by the removal of the first
toe. The third is still the largest, and forms the
center of support ; the second and third are of equal
size and form a pair arranged on each side of it.
The fifth is an odd toe with nothing to balance it on
the inner side of the foot. There is no trace of the
symmetry around a line drawn between the third
and fourth toes, or of the equality of these two which
is seen in Artiodactyles. By referring to the dia-
gram at p. 15 (Fig. 1), it will be easily understood
ITS ANCESTORS AND RELATIONS.
31
that A is not converted into B by merely taking
away the digit I.
It can hardly be supposed that the change took
place suddenly from a five-toed to a four-toed fore-
foot, and indications have been discovered of inter-
mediate forms (Eoliippus of Marsh) in which a rudi-
mentary first toe, represented only by the metacar-
pal bone, existed, but these have not yet been fully
described.
The hind foot of Hyracotherium presents a still
greater modification, both the outer digits, first and
fifth, having disappeared. The three middle toes,
Fig. 3. — Grinding surface of upper molar tooth (very
slightly worn). A, Phenacodus. B, Hyracotherium.
C, Anchitherium. a, antero-external eusp ; b, antero-
internal cusp ; c, postero-external cusp ; d, pos-
tero-internal cusp.
symmetrically disposed to the axis of the third, are
alone present. This is the condition of the hind foot
of all known true Perissodactyles of the Eocene and
Miocene epoch, and of the greater number of those
32 THE HORSE.
still existing, the horse alone having advanced to a
still more specialized state.
The teeth of Hyracotherium and its allies are the
same in number as in Phenacodus — the same, in
fact, as in the vast majority of Eocene mammals j
but they begin to show more distinctly, especially in
the grinding surfaces of the molars, a pattern in
which the groundwork of all the subsequent com-
plex modifications can be clearly traced (Fig. 3, B).
The four larger corner cusps are distinct, but the
intermediate ones are assuming the form of ridges
or crests connecting the two anterior and the two
posterior cusps respectively. These ridges are of a
curved or sinuous form, and are not placed quite
transversely, but have their inner ends inclining
backwards. It will be usefid to become thoroughly
acquainted with this pattern, as it is the key to all
others which will be hereafter spoken of.
In deposits of corresponding and more recent age
to those in which the remains of Hyracotherium
were found, immense numbers of bones and teeth
have been discovered, indicating a variety of spe-
cies more or less diverging in details, although con-
structed in the main upon the same type, the best
known of which are included in the genera Lo~
phiodon of European and Hyrachyus of American
formations. Of the latter, remarkably complete
ITS ANCESTORS AND RELATIONS. 33
skeletons have been discovered and fully described
by Leidy, so that its osteology is now completely
known. A few further stages of modification lead
to the Palceotherium of the Paris basin (late Eocene),
an interesting form from its association with the
illustrious Cuvier, who in 1804 established its exist-
ence, and by comparison of its bones with those of
all known recent species of animals, demonstrated
for the first time to the satisfaction of the scientific
world that animals had inhabited the earth other than
those now found upon its surface. By this dem-
onstration he laid the foundation of the study of
palaeontology of vertebrated animals — a study which
has developed in this comparatively short period of
time to such a marvelous extent, and which has still
before it a future of unbounded promise.
By the time that the Palaaotherium appeared, the
group of Perissodactyles was already breaking up
into different families by the gradual change in vari-
ous directions from the primitive Lophiodont type.
Some were passing step by step into tapirs, which
still exist and retain much more of the original char-
acters of the primitive ungulates of the Eocene
period than any of the others now remaining on
the earth, having indeed continued practically un-
changed since the Miocene times; while almost all
other mammalian forms which existed then have
34 THE HORSE.
either become extinct or undergone extensive modi-
fication. In the structure of their feet they scarce-
ly differ from Hyracotherium. They are, in fact,
typical old conservatives, which have scarcely de-
parted in any way from the manners, customs, or
structure of their ancestors. They appear to be ani-
mals tending to extinction, for, though formerly
having a wide range of distribution through the con-
tinents of America, Europe, and Asia, they are now-
only found at two rather isolated parts of the
world — i.e., South and Central America and the
Malay region — and they are by no means numerous
either in species or individuals.
A second branch of the group can be traced
through such forms as Hyracodon, Aceratherkim,
and Aphelops to the modern rhinoceroses, which
in many respects are more specialized than the
tapirs. They have but three toes upon each foot,
and the teeth have been considerably changed,
some species having lost all the incisors or cutting
teeth of the front of the mouth. They have, more-
over, acquired the peculiarity of wearing one or
two large horns upon their noses, which the early
species of the family did not possess.
Somewhat allied to the rhinoceroses were some
remarkable animals which flourished in the early
Miocene time in North America, to various modifi-
ITS ANCESTORS AND RELATIONS. 35
cations of which the names Menodus, TifanotJierium,
MegaceropSj Brontotherium, and Symborodon have been
given. They were of gigantic size, with a large head,
having on the face a pair of stout, diverging, osseous
protuberances, like the horn-cores of ruminants.
Their fore-feet had four and their hind feet had
three short stout toes. Also, out of the hue of descent
of any existing Perissodactyles was the remarkable
MacraucJienia, a very specialized form, which existed
in South America, apparently to Pliocene times, and
then entirely disappeared from a world in which the
conditions necessary for its well-being no longer ex-
isted, unless indeed we may suppose that the life of a
species, like that of an individual, comes to an end by
virtue of some inherent tendency which is one of the
essential attributes of its existence. Leaving these
and numerous other collateral branches which have
left no representatives, we may pass to the third ex-
isting division, the most important in regard to the
present subject.
Allied to Palaeotherium, but probably more on
the direct line of descent between Hyracotherium
and the forms to be mentioned presently, was a small
animal to which the name of Paluplotlierium has been
given, of which numerous teeth and bones have been
found in the beds of Upper Eocene age at Hord-
well in Hampshire, in the Isle of Wight, and in va-
36 THE HORSE.
rious parts of France and Germany. Another form
associated by Cnvier with Palaeotheriuin, the first
known remains of which were f onnd in the neigh-
borhood of Orleans and hence called P. aurelianense,
was by H. von Meyer separated generically under
the name of AncJiitherium. It flourished in the Mio-
cene age, both in Europe and America, under many
minor modifications, and is generally looked upon
as in the direct line of ancestry of the modern
Equiclce, which the true Palceotherium probably was
not. One of the most striking characters by which
it differs from Hyracotherium is the complete loss
of the fifth digit of the fore-foot, all the extremities
being alike in possessing only the three middle toes
(second, third, and fourth of the typical condition),
all reaching to the ground, but with the central one
(the third) longer than the others (see Fig. 4). The
two bones of the forearm (radius and ulna) and the
two of the leg (tibia and fibula) were still quite dis-
tinct. The pattern of the grinding surface of the
molar teeth (see Fig. 3, C, p. 31) had undergone some
further modifications from that of Hyracotherium,
which will be alluded to later on when describing the
dentition of the horse. The Anchitherium was suc-
ceeded in the Pliocene period, in America, Europe,
and Asia, by animals which have been named Hip-
parion, Hippotlierium, Proiohippus, and Pliohippus, of
ITS ANCESTOKS AND EELATIONS.
37
which there were many kinds, differing slightly in
form and proportions, and in the characters of the
Fig. 4.— Side and front view of the bones of the left
fore-foot of Anchitherium (without the upper row of
carpal bones), t, trapezium; tr, trapezoid; go,
magnum ; one, unciform ; 2m, second metacarpal ;
3w, third metacarpal ; Am, fourth metacarpal ;
5m, rudiment of the fifth metacarpal ; p', p", p" ,
the first, second, and third phalanges of the mid-
dle (third) digit, The upper surface of third me-
tacarpal is represented for comparison with Figs.
5 and 6, showing gradual change of form. (From
Gaudry. )
enamel foldings of the molar teeth, but resembling
each other in the structure of the feet. The lateral
toes (second and fourth), though containing the full
38
THE HOESE.
number of bones, were much reduced in size, and
did not reach to the ground (see Fig. 5), but were sus-
pended to the outside of, and rather behind, the large
middle one, like the rudimentary outer toes of the
.a- one*
Fig. 5. — Side and front view of the bones of the left
fore-foot of Hipparion. s, and s', upper and lower
sesamoid bones. (From Gaudry.)
deer or the short first digit (" dew-claw ") of the dog.
Well-preserved remains of animals with this struct-
ure of foot have been met with abundantly at Pi-
kermi, in Greece, and also in most of the deposits of
ITS ANCESTORS AND RELATIONS.
39
corresponding age in the southern parts of France
and Germany. Their former existence in England
lr. CfO one.
Yig, 6.— Side and front view of the bones of the left
fore-foot of the horse. Letters as in Figs. 4 and 5.
(From Gaudry. )
is only attested by scanty fragments found in the
red crag of Suffolk. Horses, or rather horse-like
creatures, with this structure of feet were no longer
4
40 THE HOESE.
met with when the Pleistocene, or latest geological
period, set in ; but then, for the first time, appeared
the true horse, in its development exactly or very
nearly as we know it now. The outer toes (second
and fourth) were reduced to rudiments of the meta-
carpals or metatarsals entirely concealed beneath
the skin, while the middle or third toe was greatly
elongated and had its last bone or ungual phalanx
much expanded in breadth (Fig. 6). At the same
time, the stability of the forearm and leg was in-
creased by the two bones contained in each limb in
the primitive forms becoming completely fused into
one. Even since the Pleistocene period a change
has taken place, as in horses of the present time the
lateral rudimentary metapodials, or " splint bones "
of veterinary anatomy (Fig. 6, 2m and 4w)> though
independent bones in the young animal have a
great tendency to become united with the large mid-
dle bone as life goes on ; but in horses of the pre-
historic or still earlier periods they are always found
free, and were also relatively longer than they are
now.
These modifications of the limbs thus gradually
acquired in the course of time must have been asso-
ciated with gradually increased speed in running,
especially over firm and unyielding ground. Short,
stout legs and broad feet, with numerous toes, spread-
ITS ANCESTORS AND RELATIONS. 41
ing apart from each other when the weight of the
creature is borne on them, are sufficiently well
adapted for plodding deliberately over marshy and
yielding surfaces, and the tapir and the rhinoceros,
which in the structure of the limbs have altered but
little from the primitive Eocene forms, still haunt
the borders of streams and lakes and the shady
depths of forests, as was probably the habit of their
ancient representatives ; while the horses are all in-
habitants of the open plains, for life upon which
their whole organization is in the most eminent de-
gree adapted. The length and mobility of the neck,
position of the eye and ear, and great development
of the organ of smell, give them ample means of
becoming aware of the approach of enemies ; while
the length of their limbs, the angles the different
segments form with each other, and especially the
combination of firmness, stability, and lightness in
the reduction of all the toes to a single one, upon
which the whole weight of the bodv and all the
muscular power are concentrated, give them speed
and endurance surpassing that of almost any other
animal.
Remarkable changes in the structure and mode
of growth of the teeth, which will be described in
detail later on, have taken place pari passu with the
modifications of the limbs and added greatly to their
42 THE HORSE.
power as organs of mastication, and enabled their
possessors to find their sustenance among the com-
paratively dry and harsh herbage of the open plains,
instead of being limited to the more succulent vege-
table productions of the marshes and forests in
which their predecessors mainly dwelt.
The structural transitions from the diminutive
Hyracotherium of the early Eocene period to the
modern horse have been accompanied by a gradual
increase of dimensions. The Miocene Anchitherium
was of the size of a sheep. The Pliocene Hipparion
and its allies were as large as modern donkeys ; and
it is only in the Pleistocene period that Equidcv ap-
peared that approached in size the existing horse,
the largest races of which are all the products of
good feeding and selective breeding since it has be-
come a domesticated animal.
It will be seen from what has been already said
that the history of the Perissodactyles as a group
offers many points of interest to the naturalist.
Among these are its rapid extension and separation
into various modifications, all containing numerous
minor variations ; the complete extinction of many
of these, and the survival of three branches only, all
of which (except the two domesticated species of the
equine branch, which have been largely multiplied
and diffused by man's agency) are poor in genera
ITS ANCESTOES AND EELATIONR. 43
and species and far more restricted than formerly in
geographical distribution. When we consider how
extremely imperfect our knowledge of the former
inhabitants of the earth must necessarily be, com-
pared with that of those now existing, it is remark-
able that we have already evidence enough to show
that, at any period we may select since the Middle
Eocene time, Perissodactyles were far more abun-
dant, varied, and widely distributed than they are
at present. This is the more interesting, as it is in
marked contrast with what we know of the history
of the other great division, the Artiodactyles, the
latest modification of which, especially the hollow-
horned ruminants or Bovidw (antelopes, sheep, or
oxen), are now the dominating members of the great
Ungulate order, widespread in geographical range,
rich in generic and specific variation, and numerous
in individuals.
Of the three existing families of Perissodactyles,
the least modified are, compared to their former
abundance, in the most decadent state, while the
most recently formed, and greatly modified, and
most progressive group was until very recently
bravely holding its own, in at least one region of its
former extensive range. On the great plains of the
African continent, zebras and quaggas roamed in
countless herds within the memory of living man,
44 THE HORSE.
and, except for his interference, there seemed no
reason why they might not have continued to do so
for ages yet. Explorers, hunters, and settlers, ac-
companied by the introduction of fire-arms into their
native haunts, have, however, settled their doom.
If events proceed as they are now doing, we may
safely predict that the time is not very far distant
when any living animal of the entire group of Peris-
sodactyles, except in a state of domestication, will
be a thing of the past. Under the rapidly changing
circumstances of the world, caused by the spread of
European civilization, it is not unlikely that the
most ancient form, the tapir, may yet survive all the
others, simply because it offers less inducement for
the exercise of the destructive propensities of the
modern sportsman, who is more responsible than any
one else for the change now taking place in the nor-
mal balance of animal life on the earth's surface.
In the next chapter this part of the subject will be
entered into rather more fully.
CHAPTER II.
THE HORSE AND ITS NEAREST EXISTING RELATIONS.
The tapirs (Family Tapiridcc) — Characters, species, geograph-
ical and geological distribution — The rhinoceroses (Fam-
ily Ithinocerotid(v) — The horses (Family Equidce) — Their
immediate predecessors — The hipparions or three-toed
horses of Europe and America — Existing species of horses
— The horse (Equus caballus) — Wild, domesticated, and
feral horses — Wild asses — Equus hemionus of Asia and its
varieties — The African wild ass and the domestic ass
(Equus asinus) — Striped members of the equine family —
Zebras and quaggas (Equus zebra, E. burchetti, E. grcvyi,
and E. quagga) — Hybrids or mules — Aptitude for domes-
tication only found in certain members of the family.
As shown in the last chapter, the Perissodactyle
ungulates, by various and gradually progressing de-
viations from the common original type, began at a
very early age to break up into several groups, some
of which, after undergoing a considerable degree of
specialization, have become extinct, without leaving
successors ; but three of these modified types, already
distinct at the close of the Eocene period, have con-
tinued up to the present day, gradually, as time ad-
vanced, becoming more and more divergent from each
4G THE HOUSE.
other. These are now represented by the three fami-
lies of the Tapirs, the Rhinoceroses, and the Horses.
Great as may be the differences between these ani-
mals as we see them now, we can trace their history
step by step, as shown by the fragments preserved
from former ages, farther and farther back into
time, their differences continually becoming less
marked, and ultimately blending together, if not
into one common ancestor, at all events into forms
so closely alike in all essentials that no reasonable
doubt can be held as to their common origin.
As already indicated, the first named, the tapirs,
have retained much more of the original characters
of the primitive ungulates of the Eocene period than
either of the others, and have indeed remained prac-
tically unchanged since the Miocene period; while
almost all other mammalian forms which existed
then have either become extinct or undergone ex-
tensive modification.
The Tapirs. (Family Tapiridce.)
The tapirs constitute the single genus Tapirus,
of which all the known species are much alike in ex-
ternal as well as anatomical characters. They are
rather heavy, thick-set animals, with short and stout
limbs. The fore-feet have four distinct toes, the
first (that corresponding to the thumb of man) only
ITS NEAREST EXISTING RELATIONS,
47
being absent, those that are present corresponding
to the second, third, fourth, and fifth of the typical
five-toed limb. The third toe is the longest, the
second and fourth nearly equal, and the fifth the
shortest, and scarcely reaching the ground in the or-
dinary standing position. The hind feet have three
B
til S&H ,ht : •
Fig. 7. — Plantar surface of right fore (A) and hind
(B) foot of Malay Tapir. (From Murie. Journal
of Anatomy and Physiology, vol. vi.)
toes, the middle one being the largest, and the two
others rather shorter. Each toe is incased in a dis-
tinct, somewhat oval hoof, and there is a large,
roundish, callous pad on the sole of the foot, on
which the animal rests as well as on the toes (see
48 THE HOESE.
Fig. 7). The nose and upper lip are elongated into
a flexible mobile snout or short proboscis, at the end
of which the nostrils are situated. The eyes are
rather small. The ears are of moderate size, ovate,
and erect. The tail is very short. The skin is thick
and smooth, and covered with a short and rather
scanty hairy coat.
The skull is elevated and compressed. The orbit
and temporal fossa are widely continuous, there be-
ing no true post-orbital process of the temporal bone.
The anterior narial apertures are very large, and ex-
tend high on the face between the orbits. The nasal
bones are short, elevated, triangular, and pointed in
front. Vertebrae — Cervical, 7; dorsal, 18; lumbar,
5 ; sacral, 6 ; caudal, about 12. The teeth are — In-
cisors, f ; canines, { ; premolars, f 5 and molars, -J on
each side, making a total of 42 ; thus, one tooth of
the typical dentition, the first lower premolar, is
wanting. The molar teeth of both jaws may be
briefly described, as bilophodont, or having two
transverse ridges; brachyodont, or short crowned,
and without cement.
The species of tapirs are not numerous, and are
all much alike in general form, anatomical structure,
and especially dentition, so they may be said to con-
stitute a single genus, Tapir us. The existing species
may be grouped into two sections, the distinctive
• ITS NEAREST EXISTING RELATIONS. 49
characters of which are only recognizable in the
skeleton.
(A) With a great anterior prolongation of the
ossification of the nasal septum (mesethmoid), ex-
tending in the adnlt far beyond the nasal bones, and
supported and embraced at the base by ascending
plates from the maxilla?. This section constitutes
the genus Elasmognathus of Gill. There are two
species, both from Central America.
Tapirus bairdi (Baird's tapir) : Mexico, Honduras,
Nicaragua, Costa Rica, and Panama.
Tapirus doivi (Dow's tapir) : Guatemala, Nicara-
gua, and Costa Rica.
(B) With the ossification of the septum not ex-
tending farther forward than the nasal bones. Three
species :
T. indicus (the Malay tapir) : Malay Peninsula
(as far north as Tavoy and Mergui) and the islands
of Sumatra and Borneo. T. aniericanus (T. ter-
restris, Linn.). The common South American tapir
of the forests and lowlands of Brazil and Para-
guay and the northern part of the Argentine Re-
public.
T. roulini. The Pinch aque 'or Roulin's tapir of
the high regions of the Cordilleras of Colombia
and Ecuador, 7,000 to 8,000 feet above the sea
level.
50 THE HORSE.'
The Malay tapir is the largest of the genus, and
distinguished from all others by its peculiar colora-
tion, the head, neck, fore and hind limbs being glossy
black and the intermediate part of the body white.
The demarkation of the two colors is distinctly de-
,r>m \ if |
Fig. 8. — The American Tapir (Tapirus americanus).
From a photograph by Mr. Gambler Bolton of an animal living In the
Zoological Gurdens, London.
fined. The white of the body does not quite meet
below, a median dark line intervening. All the
American species are of a nearly uniform dark brown
or blackish color when adult ; but it is a curious cir-
cumstance that when young (and in this the Malay
species agrees with the others) they are conspicuously
ITS NEAEEST EXISTING EELATIONS. 51
marked with spots and longitudinal stripes of white
or fawn color on a darker ground.
The habits of all the kinds of tapirs appear to be
very similar. They are solitary, nocturnal, shy, and
inoffensive, chiefly frequenting the depths of shady
forests and the neighborhood of water, to which they
frequently resort for the purpose of bathing, and in
which they often take refuge when pursued. They
feed on various vegetable substances, as shoots of
trees and bushes, buds and leaves. They are hunted
by the natives of the land in which they live for the
sake of their hides and flesh.
" The tapirs/' Wallace says, " form a small group
of mammals, whose discontinuous distribution plainly
indicates their approaching extinction." Tins view
is supported, and the singular fact of the existence
of so closely allied animals as the Malayan and the
American tapirs in such distant regions of the earth
and in no intervening places, is accounted for by
what is known of the geological history of the race ;
for, if we may judge from the somewhat scanty re-
mains which have been preserved to our times, con-
sisting chiefly of teeth, the tapirs must once have
had a very wide distribution. There is no proof of
their having lived in the Eocene epoch ; but by the
Middle Miocene, tapirs undistinguishable generically
from those now existing were already formed, so
52 THE HORSE.
that they share the honors with Hyomoschus or Dor-
catJierium* of being the oldest living mammalian
form. Such remains of Miocene and Pliocene age
have been found in France, Germany, and England
(Suffolk red crag). They appear, however, to have
become extinct in Europe before the Pleistocene
period, as none of their bones or teeth have been
found in any of the caves or alluvial deposits in
which those of elephants, rhinoceroses, and hippo-
potamuses occur in abundance ; but in other regions
their distribution at this age was wider than at
present, as they are known to have extended east-
ward to China, and westward over the greater part of
the southern United States of America, from South
Carolina to California. Lund also distinguished two
species or varieties from the caves of Brazil. Thus
we have no difficulty in tracing the common origin
of the now widely separated American or Asiatic
species. It is, moreover, interesting to observe how
very slight an amount of variation has taken place
in forms isolated during such an enormous period of
time. This may be owing to the extreme similarity
of the conditions of existence in a Brazilian and a
Malayan forest.
* A small Artiodactyle, somewhat intermediate in struct-
ure between a deer and a pig, found living in Western Africa
and fossil in deposits of Miocene age in Germany.
ITS NEAEEST EXISTING RELATIONS. 53
The Rhinoceroses (Family Ehinocerotklce).
The name rhinoceros (meaning in Greek "nose-
horn ") was applied by the ancients to an animal the
most striking external peculiarity of which was cer-
tainly the horn growing above its nose.
The following are the general characters appli-
cable to all the existing members of the family :
Head large. Ears of moderate size, oval, erect,
prominent, placed near the occipnt. Eyes small.
Neck short. Skin very thick, in some species consist-
ing of massive, indurated, almost inflexible, plates,
with thin soft intervals or joints, to allow of motion.
Hairy covering scanty. Tail of moderate length,
slightly tufted. Limbs stont, rather short. Three
completely developed toes, with distinct, broad,
rounded hoofs on each foot.*
All existing species have one or two horns, placed
in the middle line upon the face. When one is
present, it is situated over the conjoined nasal bones ;
when two, the hinder one is over the frontals. These
horns differ in details of structure from those of any
other animal, though belonging to the same category
of epidermic growths as the horns of oxen, as well
as nails, claws, hoofs, callosities, and warts. Their
* In some extinct species a small outer toe is present on
the fore-foot.
54 THE HORSE.
structure, as seen under the microscope, lias a great
resemblance to that of whalebone, being composed
of a solid mass of hardened epidermic cells growing
from a cluster of long dermal papilhe. The cells
formed on each papilla constitute a distinct horny
fiber, like a thick hair, and the whole are cemented
together by an intermediate mass of cells which
grow up from the interspaces between the papilhe.
It results from this thai the horn has the appearance
of a mass of agglutinated hairs, which, in the newly-
growing part, at the base, readily fray out on destruc-
tion of the softer intermediate substance; but any
one acquainted with the structure and mode of
growth of true hairs will see that the fibers differ
from them in growing around a long tree papilla
on the surface of the derm, instead of from a very
short papilla sunk deeply in a follicular involution
of the same. These horns are really warts, which
have assumed a solid and definite form, and the
stages by which they may have developed are illus-
trated in the irregularly-shaped supplementary horns
which are sometimes found either on the face or
other parts of the body, the product of some local
abnormal condition of the skin.*
* See :i case of an African rhinoceros with a third horn
described in the Proceedings of the Zoological Society of Lon-
don, L889, p. 418.
ITS NEAREST EXISTING RELATIONS. 55
When fully developed, the horns are of a more or
less conical form usually curved backwards at their
ends, and often grow to a great length (three or even
four feet), but they are constantly worn away at the
ends and sides by being rubbed against trees or
stones, and are continually growing at the base.
Their length and shape are, therefore, subject to
considerable variation, even in the same individual
at different times, and so cannot be depended upon
for the distinction of species, as some naturalists
have imagined. Though not normally shed, they
are occasionally torn off at the base,* in which case
a new horn will grow in its place, although, if the
matrix, or portion of the skin to which it is attached,
is much injured, it may assume a more or less irreg-
ular shape.
As regards the dentition, the incisors are varia-
ble, generally reduced in number, and often quite
rudimentary and entirely disappearing at a very
early age.f The canines in existing species are
* This happened in 1870 to the male Indian rhinoceros
still living in the gardens of the Zoological Society of Lon-
don, in an effort to raise with its horn a strong transverse iron
bar at the lower part of the railings of the inclosure in which
it was confined.
t It is difficult to see what advantage the great African
two-horned rhinoceroses can find in the complete absence of
their front teeth, but this is one of those numerous cases in
which we must be content to acknowledge our ignorance and
wait for the explanation.
5
56 THE HORSE.
absent * In respect to the front teeth, therefore, a
very marked amount of specialization has taken
place. On the other hand, the cheek teeth are re-
tained in full normal numbers — viz., four premolars
and three molars on each side above and below, all
in contact, and closely resembling each other, except
the first, which is much smaller than the rest, and
often lost early in life. The others gradually in-
crease in size from before backwards up to the
penultimate, which is the largest. The upper mo-
lars have a very characteristic pattern, admirably
adapted for bruising and crushing coarse vegetable
substances, and which is clearly a modification of
the pattern already seen in the corresponding teeth
of Hyracotherium. The lower molars are of simpler
form, the two transverse ridges being curved into
a crescentic form. In neither case are the deep de-
pressions between the ridges filled up with cement,
as in the horse.
The skull is elongated and elevated posteriorly
into a transverse occipital crest. It has retained its
primitive condition in possessing no post-orbital
processes or any separation between the orbits and
temporal fossae. The nasal bones are large and
stout, co-ossified, and standing out freely above the
* It should be stated that certain teeth, regarded above as
incisors, are considered by some zoologists as modified canines.
ITS NEAREST EXISTING RELATIONS. 57
premaxilhe, from which they are separated by a
deep and wide fissure ; the latter bones are very
small, generally not meeting in the middle line in
front, often quite rudimentary, a specialization con-
current with the loss of the upper incisor teeth. The
brain cavity is very small for the size of the skull.
Vertebras — Cervical, 7 ; dorsal, 19-20 • lumbar, 3 •
sacral, 4 • caudal, about 22.
The Rhinocerotidw are all animals of large size,
but of little intelligence, generally timid of disposi-
tion, though ferocious when attacked and brought
to bay, using the nasal horns as weapons, with which
they strike and toss their assailants. Their sight is
dull, but then* hearing and scent are remarkably
acute. They feed on herbage, shrubs, and leaves
of trees, and, like so many large animals which in-
habit hot countries, sleep the greater part of the day,
being most active in the cool of the evening or even
during the night. They are fond of bathing or wal-
lowing in the mud. None of the species have been
domesticated. The family once contained many
more species and was much more widely distributed
than at present. As already indicated, our knowl-
edge of them is as yet but fragmentary, though con-
stantly augmenting, especially by discoveries made
in the Tertiary deposits of North America, a region
from which they all died out long ago, though, judg-
58 THE HORSE.
ing from the evidence at present available, this was
the locality in which they first made their appearance.
In the Eocene formations of the Rocky Mountains
are found the remains of numerous modifications of
the primitive Perissodactylc type, from which the
rhinoceroses may have originated. In the Lower
Miocene a form called Jh/nirodon by Leidy already
presented many of the characteristics of the family,
though, especially as regards the dentition, still in
a very generalized condition. It had, however,
already lost the fifth toe of the fore-foot. The next
stage of specialization is represented by Aceratheri-
um and Aphelops, found in the Miocene of Europe
and America, which still, like the last, show no sign
of having possessed a nasal horn. The former
differs from the existing species, and also from .////-
racodon, in having four toes on the anterior limb
instead of only three. At the same period forms
occurred {IHceratherium, Marsh) which show a pair
of lateral tubercles on the nasal bones apparently
supporting horns side by side. These, however, soon
disappeared and gave way in the Old World to species
with one or two horns in the median line, a stage of
development which apparently wras never reached in
America. In the Pliocene and Pleistocene of Europe
and Asia numerous rhinoceros remains have been
found, all more or less nearly related to the existing
ITS NEAREST EXISTING RELATIONS. 59
species. The present African two-horned type was
already represented in the early Pliocene of Greece
by R. pachygnathus, the skeleton of which is described
by Gaudry as intermediate between the existing R.
birornis and R. simus. As many as three species
were inhabitants of the British Isles, of which the
best known is the Tichorhine or woolly rhinoceros,
R. antiquitatis of Blumenbach, R. tichorhinus of other
authors, nearly whole carcasses of which, with their
thick woolly external covering, have been discovered,
associated with those of the mammoth, preserved in
the frozen soil of the north of Siberia, and which, in
common with some other extinct species, had a solid
median wall of bone supporting the nasals. From
this peculiarity it has been inferred that the horns
were of size and weight surpassing those of the
modern species. The one-horned Indian type was
well represented under several modificatons (R.
simlensis, R. palceindicus, etc.) in the Pliocene deposits
of the sub-Himalayan region, and forms more allied
to the African bicorn species have also been found in
a fossil state in India. R. sclileiermaclieri of the late
European Miocene in some features, especially in
possession of incisor teeth and two horns, resembled
the existing Sumatran rhinoceros, but it differed in
important cranial characters.
The existing species of rhinoceros are naturally
60 THE HORSE.
grouped in three sections, which some zoologists con-
sider of generic value.
I. Rhinoceros proper. The adults with a single
large compressed incisor tooth above on each side,
and occasionally a very small lateral one ; below, a
very small median, and a very large, procumbent,
pointed, lateral incisor (or canine?). Nasal bones
pointed in front. A single nasal horn. Skin dis-
posed in very massive, definitely arranged armor-like
plates, with soft interspaces or joints between them.
There are two well-marked species of one-horned
rhinoceros :
1. The Indian rhinoceros, R. unicornis of Lin-
naeus,* the largest and best known, from being
the most frequently exhibited alive in England, is at
present only met with in a wild state in the Terai
region of Nepal and Bhutan, and in the upper valley
* Many authors use Cuvier's name, R. indieus, in prefer-
ence to this, on the ground that there are more than one
species with one horn, forgetting that the name substituted is
equally inconvenient, as more than one species live in India.
The fact of a specific name being applicable to several mem-
bers of a genus is no objection to its restriction to the first
to which it was applied, otherwise changes in old and well-
received names would constantly have to be made in conse-
quence of new discoveries. Ill-considered attempts at precis-
ion of nomenclature are often sources of confusion and future
difficulty. As Huxley has truly said, " It is better for science
to accept a faulty name which has the merit of existence,
than to burden it with a faultless newly-invented one."
ITS NEAREST EXISTING RELATIONS.
61
of the Bramaputra or province of Assam, though it
formerly had a wider range. The first rhinoceros
seen alive in Europe since the time when they, in
common with nearly all the large remarkable beasts
of both Africa and Asia, were exhibited in the Roman
v
' \XMfk ■■>>/'
Fig. 9. — Indian Rhinoceros (Rhinoceros unicornis).
From a photograph by Mr. Oambier Bolton of an animal living in the
Zoological Society's Gardens. In wild animals the horn often grows to
a greater length.
shows, was of this species. It was sent from India
to Emmanuel, King of Portugal, in 1513 ; and from
a sketch of it taken in Lisbon, Albert Durer com-
posed his celebrated, but rather fanciful, engraving,
which was reproduced in so many old books on
natural history.
62 THE HORSE.
2. The Javan rhinoceros (B. sondaicus, Cuvier)
is distinguished by smaller size, special characters of
the skull and teeth, and different arrangement of the
plications of the skin, especially in the deep depres-
sion which runs upwards and backwards from the
middle of the side of the neck, passing over the back,
joining its fellow on the opposite side, and thus
isolating a plate proper to the neck from the great
shoulder-plate. In the Indian rhinoceros (Fig. 9) this
fold or depression does not pass over the back, but
curves backwards and is lost above the shoulder.
This species has a more extensive geographical range
than the last, being found in the Bengal Sunderbuns
near Calcutta, Burmah, the Malay Peninsula, Java,
Sumatra, and probably Borneo. A hornless rhinoc-
eros (R. inermis) which has been described is sup-
posed to be the female of this species, but this is a
point which requires further investigation.
II. Ceratorhinus. The adults with a moderately-
sized compressed incisor above, and a laterally-placed
pointed procumbent incisor below, which is some-
times lost in old animals. Nasal bones narrow and
pointed anteriorly. A well- developed nasal horn and
a small horn behind it, separated by a considerable
interval. The skin thrown into folds, but these are
not so strongly marked as in the former section.
The smallest living member of the family, the Suma-
ITS NEAREST EXISTING RELATIONS. 63
tran rhinoceros (R. sumatrensis, Cuv.), belongs to
this group. Its geographical range is nearly the
same as that of the Javan species, though not extend-
ing into Bengal ; but it has been found in Assam,
Chittagong, Burmah, the Malay Peninsula, Sumatra,
and Borneo. It is possible that more than one
species have been confounded under this designation,
as two animals now living in the London Zoological
Gardens present considerable differences of form and
color.
III. Atelodus. In the adults, the incisors are
quite rudimentary or entirely wanting. Nasal bones
thick, rounded, and truncated in front. Two horns,
both well developed and in close contact with each
other. Skin thick but smooth, without any definite
thickened plates or permanent folds.
The two well-marked species are peculiar to the
African continent :
1. The common two-horned rhinoceros (R. bicor-
nis, Linn.) is the smaller of the two, with a pointed,
prehensile upper lip. It ranges through the wooded
and watered districts of Africa, from Abyssinia in
the north to the Cape Colony, but its numbers are
yearly diminishing owing to the inroads of European
civilization, and especially to the persecutions of
English sportsmen. It feeds exclusively upon leaves
and branches of bushes and small trees, and chiefly
64 THE HOKSE.
frequents the sides of wood-clad rugged hills. Spec-
imens in which the posterior horn has attained a
length as great as, or greater than, the anterior horn
have been separated under the name of E. keitloa,
but, as already mentioned, the characters of these
appendages are too variable to found specific distinc-
tions upon. The two-horned African rhinoceros is
far more rarely seen in menageries in Europe than
either of the three Indian species, but one has lived
in the gardens of the London Zoological Society
since 1868. Excellent figures from life of this and
the other species are published in the ninth volume
of the Transactions of the Society.
2. Burchell's, or the square-mouthed rhinoceros
(R. simus), sometimes called the white rhinoceros,
though the color (dark slate) is not materially dif-
ferent from that of the last species, is the largest
of the whole group, and differs from all the others
in having a square, truncated upper lip, and a wide,
shallow, spatulate form of the front end of the lower
jaw. In conformity with the structure of the mouth,
this species lives entirely by browsing on grass, and
is therefore more partial to open countries or districts
where there are broad grassy valleys between the
tracts of bush. It is only known in the regions south
of the Zambesi, and owing to the causes indicated
above has of late years become extremely scarce;
ITS NEAREST EXISTING RELATIONS. 65
indeed, the time of its complete extinction cannot
be far off, if indeed it has not already arrived. No
specimen of tins species has ever been brought alive
to Europe, and very few examples are to be seen in
our museums. The flesh of both species of African
rhinoceroses is considered very good eating by the
natives of the countries in which they live, being,
according to Selous,* " something like beef, but yet
having a peculiar flavor of its own. The part in
greatest favor among hunters is the hump, which, if
cut off whole, and roasted, just as it is, in the skin, in
a hole dug in the ground, woidd be difficult to match
either for juiciness or flavor."
Before leaving the rhinoceroses, a huge creature
belonging to the family, to which the name of Elas-
motherium has been given, shoidd be mentioned. It
is only imperfectly known by fossil remains found in
Pleistocene deposits in Russia ; but it is interesting
on account of the remarkable degree of specialization
its molar teeth had attained, far beyond that of the
existing rhinoceroses, and comparable in the length
of the crowns and the complex folding of the enamel
to that of the horses of the same or later period,
though on a very much larger scale. It affords a
good illustration of the fact previously mentioned,
* See F. C. Selous, Proceedings of the Zoological Society of
London, 1881.
66 THE HORSE.
that the most highly specialized members of a group
are not always those that survive the longest.
The Horses. (Family Equidce.)
As has been already stated, at about the time
of the world's history when the Miocene was pass-
ing into what we term the Pliocene epoch, there
were no true horses in exactly the sense in which
we use the word now, bub horse-like animals were
extremely abundant both in America and the Old
World, differing from existing horses in details of
teeth and skeleton, especially in the presence of three
toes upon each foot, a large middle toe and a smaller
one, not reaching to the ground, placed on each side
of it. To these animals, the step from the Anchi-
therium of the early Miocene, mentioned in the last
chapter, was not a very great one.
Unfortunately, when remains of this type were
first discovered, two generic names were given to
them almost simultaneously — Hipparion and Hippo-
therium, the former being a diminutive of hippos,
the Greek for "horse"; the latter a compound of
hippos and titer ion, a wild beast, Latinized to theri-
um, a termination very commonly employed in mod-
ern scientific language when coining new appella-
tions for extinct animals. The first name was given
ITS NEAREST EXISTING RELATIONS. 67
by the French palaeontologist Christol ; * the latter
by Kaup of Darmstadt. t Although Christol's ap-
pears to have the actual priority, and has been ex-
tensively used, especially in France and England, it
does not seem to have been accompanied when first
brought out by any clear description, and is therefore
not acknowledged by many zoological authors, espe-
cially in Germany and America, where Hippotherium
takes its place. Protoh ippus and various other names
have been proposed for other modifications (differing
chiefly in tooth structure) of animals in the same gen-
eral phase of evolution. The great variety of these
forms may be gathered from the fact that in a recent
memoir Professor Cope has described fifteen spe-
cies of Hippotherium, which he considers to be quite
distinct from each other, from North America alone. f
The term " Hipparion " has become so well known,
even beyond the limits of strictly scientific literature,
that it may be conveniently used as a common name
for all the three-toed horse-like animals which im-
mediately precede the existing Hqidce, reserving
Hippotherium, Protohippus, etc., for generic modifica-
tions capable of exact zoological definition.
* Ann. Sci. Indust. Mid. France, vol. i. p. 180 (1832).
t Jahrbuch fur Mineralogie, etc., 1833, p. 327.
X "A Review of the North American Species of Hippothe-
rium," Proc. American Philosophical Society, 1889.
68 THE HORSE.
In the quarries of Pikermi, in Greece, an immense
number of remains of large animals, now entirely
extinct, have been discovered and made known to us
mainly by the admirable memoir published upon
them by the eminent French palaeontologist, Albert
Gaudry.* These animals include monkeys, civets,
hyenas, wild boars, rhinoceroses, antelopes of various
kinds, a great giraffe-like creature called HeJlado-
tlierhim, and hipparions in such multitudes as to
show that these animals must have wandered over
the plains of Europe in great herds, comparable to
those of the wild asses of Tartary and the zebras of
South Africa of recent times. The collection made
by Gaudry alone consisted of 1,900 bones, belonging
to at least twenty-four individuals. They have also
been found in similar numbers at Eppelsheim in
Germany, and at Mont Leberon and in Vaucluse in
the south of France.
One of the principal characteristics of the skeleton
of the Pikermi hipparion is the presence of a con-
siderable depression or pit upon the side of the face
in front of the orbit or cavity for the eye. Although
such a pit is not found in any of the existing species
of horse, it was not infrequent in many extinct
forms, and varied in them in size and depth. It so
closely resembles a similar depression, found in the
* Animaux fossiles et Geologie de VAttique, 1862.
ITS NEAREST EXISTING RELATIONS. 69
same situation in many species of deer and antelopes,
which lodges a glandular infolding or pouch of the
skin called the "suborbital gland/' "crumen," or in
French " larmier/' that there can be little doubt but
that it had the same purpose in the hipparion. The
gland in the existing animals that possess it secretes
a peculiar oily, odorous substance, the scent of which
enables the animals provided with it to recognize
each other even at immense distances, the faculty of
smell being also developed to a wonderful degree.
At certain seasons of the year the glands are es-
pecially active, and their position is such that when
the animal is feeding particles of the odorous secre-
tions will fall on and adhere to the herbage around,
and thus afford indications to any other animals of
the same species that may for some time afterwards
pass over the same ground.
The presence of this gland in the hipparion and
its absence in the more modern Equidce has been
given as a reason for supposing that the latter are
not the direct descendants of the former, but must
have been derived from some other form in which
such a specialization had not been developed. This,
of course, is probable ; but it must not be forgotten
that very slight changes in habits, or the increased
power and use of other senses than that of smell,
may have diminished the value of the information
70 THE HORSE.
afforded by means of this gland, and ultimately led
to the elimination of the organ itself. It may be
that a change from a life habitually passed in forests
or scrub to one in open plains would be sufficient to
account for such a modification in structure. In
any case, it is one which must be very easily brought
about, without any other great changes, as the mod-
ern ruminants show, being present or absent in them
quite irrespectively of real affinity, as indicated by
more fundamental and less superficial and adaptive
structural characters. It would be interesting to make
a careful microscopical examination of the skin of
this region in all existing species of Uquidce, to as-
certain whether any traces of the gland can be found •
for it is present in a most rudimentary condition,
without showing any impression on the surface of the
bone below in several of the existing Bovidce, the
sheep, for instance. In this animal, its place in the
economy of life is supplied by the curious little bot-
tle-like glandular pouches placed between the toes.
Another easily-recognized distinction between
the hipparion and all modern horses is seen in the
structure of the upper molar teeth. The anterior
inner cusp of the primitive form (Fig. 10, a.i.) con-
stitutes a distinct column instead of being, as in the
horse, united for its whole length with the rest of the
tooth. The foldings of the enamel are also devel-
ITS NEAEEST EXISTING RELATIONS. 71
oped to a remarkable extent of complexity, These
characters cannot be clearly nnderstood until the
details of the structure of the teeth, to be explained
in the next chapter, are known ; but they are suffi-
cient to enable any one conversant with them to
recognize a single molar of an hipparion from that
of any of the existing species, and to show that the
Fig. 10. — Section of upper molar tooth of hipparion,
from the Red Crag of Suffolk, a.i, anterior inter-
nal column completely isolated from the main mass
of dentine ; p.i, posterior internal column. The
uncolored portion is the dentine, the shaded part
the cement, and the black line separating these
two the enamel. Compare with Fig. 21 , c, p. 125.
horse-like teeth found occasionally among the debris
of former Miocene or Pliocene formations in the
Red Crag of Suffolk belong to animals of this group.
These dental characters, and also details in the
structure of the bones of the feet, have led even
more conclusively than the presence of the suborbital
depression to the view that the hipparion, or, at all
events, the European Htppotherium gracile, was not
6
72 THE HOESE.
on the direct line of descent of the modern horses,
but that it was a form which, having attained a con-
siderable degree of specialization in some particulars,
a wide geographical distribution and great abun-
dance of individuals, became, as has so often hap-
pened in similar cases, extinct without direct descend-
ants from causes which we at present cannot divine.
Perhaps an inability to lose the useless outer toes
may have given it a disadvantage in a severe com-
petition for existence with otherwise closely allied
forms, which had already adopted the style of foot
which clearly shows itself the best for the existing
requirements of the race.
Judging from tooth-structure alone, a very per-
fect series of modifications from Anchitherium to the
modern horses can be shown through various species
of the American genera called Merychippus and
Protohippus, without the intervention of the special
characteristics of hipparion ; but, unfortunately, of
many of these forms, the bones, and especially those
of the limbs, are known very imperfectly or not at
all. There is, however, already enough to show that
it is by no means impossible that America may have
been the cradle of all the existing Equidce, as it seems
to have been of such apparently typical Old World
forms as rhinoceroses and camels, and that they
spread westward by means of the former free com-
ITS NEAREST EXISTING RELATIONS. 73
munication between the two continents in the neigh-
borhood of Behring's Straits, and, having prevailed
over the allied forms they found in possession, totally
disappeared from the country of their birth until
re-introduced by the agency of man. This supposi-
tion, based upon the great abundance and variety
of the possible ancestral forms of the horse which
have lately been discovered in America, may be at
any time negatived by similar discoveries in the Old
World, the absence of which at the present time can-
not be taken as any evidence of their non-existence.
In a popular exposition of this subject it would
be out of place to give an account of the views, more
or less crude, which have been put forth by the vari-
ous zoologists who have lately exercised much labor,
patience, and thought in endeavoring to investigate
the exact lines of descent of the different species and
even breeds of the existing horses from those of
earlier periods. In the first place, they would only
be intelligible to any one possessing a full knowledge
of the minute anatomical characters on the compari-
son of which the results are based ; but what is of
still more consideration, the conclusions from all
these researches can be looked upon at present as
provisional only, being founded upon such imperfect
materials as exist as yet in our collections, and liable
to be modified at any moment by fresh discoveries
74 THE HOUSE.
which may be expected to be made from time to
time.
That the science of paleontology has a great
future before it has already been intimated. The
recesses of the earth still teem with riches in untold
numbers. When they have been brought to the
light of day, their geological antiquity and their
anatomical characters will offer a fruitful field for
investigation and speculation. The harvest is indeed
abundant and the laborers hitherto few. The excel-
lent work done in this subject by Marie Pavlow, of
Moscow, is therefore particularly interesting, as
showing for the first time in the history of this
branch of science that women are equally competent
with men to enter into the field and join in gather-
ing the golden grains of knowledge.*
* The following are some of the principal works from
which fuller information concerning the palaeontology of the
EquiddB can be obtained :
E. Cope: "The Perissodactyla " (American Naturalist,
Nov. 1887, p. 985). Numerous other memoirs by the same
author in American scientific periodicals.
A. Ecker : "Das Europaische Wildpferd und dessen Be-
ziehungen zum domesticirten Pferde" (Globus, Band xxxiv.
1878).
A. Gaudry: Ancetres de nos Animaux, 1888; Les Enchaine-
ments du Monde animal, 1878; Animaux fossiles du Mont-
Lcberon, 1873 ; Geologie de VAttique, 1862-1867.
W. Kowalevski: "Sur YAnchitheri urn aurelianense et sur
l'histoire paleontologique des Chevaux" (Mem. de VAcad. Im-
per. de St.-Petersbotirg, 1873).
ITS NEAREST EXISTING RELATIONS. 75
Existing Species of Equidce.
The members of the family Equidm existing at
the present time upon the earth are generally con-
sidered to belong to one genus, that designated
Equus by Linnasus. As, however, a genus is a
merely artificial assemblage of allied animals estab-
lished for the convenience of nomenclature, zoologists
differ greatly among themselves as to the limits that
J. Leidy : Extinct Vertebrate Fauna of the Western Terri-
tories, and other memoirs.
R. Lydekker : Various memoirs and Catalogue of Fossil
Mammalia in British Museum, Part III., 1886.
Forsyth-Major: "Beitrage zur Geschichte der fossilen
Pferde," 1877 (Schweizer palaontol. Gesellschaft, vol. iv.).
O. C. Marsh : "Fossil Horses in America " {American Nat-
uralist, 1874), and other memoirs.
A. Nehring : " Fossile Pferde aus Deutsehen Diluvial- Ab-
lagerungen" (Landswirthschaftl. Jahrbuch, 1884, Bd. xiii.
Heft 1, p. 81).
Marie Pavlow : fitudes sur Vhistoire jyaJeontologique des On-
gules. Moscou, i. 1887 ; ii. 1888 ; iii. 1890.
L. Riitimeyer : " Beitrage zur Kenntniss der fossilen
Pferde, " 1863 ; " Weitere Beitrage zur Beurtheilung der Pferde
der Quaternar-Epoch " (Abhand. Schweizerischen pdldont. Ge-
sellsch., 1875).
M. Schlosser: "Beitrage zur Kenntniss der Stammesge-
sehiehte der Hufthiere, und Versueh einer Systematik der Paar
und Unpaarhufe" (Morpholog. Jahrb., 1886, Bd. xii., Heft 1).
M. Wilekens : " Forschungen auf dem Gebiete der Palaon-
tologie der Hausthiere" (Biol. Centralblat., 1889).
J. L. Wortman : " On the Origin and Development of the
Existing Horses " (Kansas City Review of Science, 1882, Nos.
2 and 12).
76 THE HOESE.
should be assigned to such a group, and there is a
considerable tendency to break up the old and larger
genera into smaller ones, if any characters can be
found by which certain of the species can be associ-
ated together and distinguished from the others. In
this way, the genus Equus has been separated into
Equns proper, Asinus, and Hippotigris, the former^
containing the horse alone, the second the asses, and
the third the zebras. The great inconvenience of
altering the limits of genera is that, as the name of
the genus is part of the name by which (in the pre-
vailing binomial system of zoological nomenclature)
the animal is designated in scientific works in all
languages, every change in the limits of a genus in-
volves some of those endless changes in names which
are among the greatest causes of embarrassment in
the study of zoology in modern times, and do so
much to repel beginners from entering upon it*
Although it may be convenient to recognize that
the horse has special characters by which it is distin-
guished from the rest of the group, and that the
others are all more nearly allied to each other than
they are to it, and that the zebras, though otherwise
* The name of the genus, it must be remembered, in the
binomial system corresponds to the surname or family name
of persons of civilized nations, but in zoology it always pre-
cedes the specific name, which corresponds to our prename
or Christian name.
ITS NEAEEST EXISTING EELATIONS. 77
closely related to the asses, are distinguished from
them and associated together by their style of color-
ing and geographical distribution, it scarcely seems
desirable that such distinctions should be made the
ground of difference of generic appellation, and they
will in this work all be spoken of as members of the
genus Equus.
The Horse (Equus cabattus, Liun.) is distin-
guished from all the others by the long hairs of the
tail being more abundant and growing quite from
the base as well as the end and sides, and also by
possessing a small bare callosity on the inner side of
the hind leg, just below the "hock" or heel-joint, in
addition to the one on the inner side of the fore-
arm, above the wrist or " knee,'7 common to all the
genus. The mane is also longer and more flowing,
the front part of it drooping over the forehead,
constituting the " forelock " ; and the ears are shorter,
the limbs longer, the feet broader, and the head
smaller.
Though the existing horses are usually not marked
in any definite manner, or only irregularly dappled
(i.e. marked with large light spots surrounded by a
darker ring), many examples are met with showing
a dark streak running along the center of the back,
like that found in all other members of the genus,
and even with dark stripes on the shoulder and legs.
78 THE HOESE.
Darwin* collected a number of cases of horses of
various breeds and countries so marked, and from
them came to the conclusion of the " probability of
the descent of all the existing races from a single
dun-colored, more or less striped primitive stock, to
which our horses occasionally revert."
Fossil remains of true horses, differing but very
slightly from those now existing, are found abun-
dantly in the most recent geological ages in almost
every part of America, from Escholtz Bay in the north
to Patagonia in the south. Whether any of these
remains should really be referred to E. cdballus or
not — that is, whether they belonged to animals which
possessed all the external characters attributed above
to that species — is, of course, doubtful. Our knowl-
edge of existing forms teaches us that closely similar
and perhaps identical skeletal and dental characters
may be associated with considerable external differ-
ences, especially in the character, distribution, and
color of the hair. If zebras were only known from
such portions of their structure as could be preserved
in a fossil state, we should never have guessed how
greatly they differed in outward aspect from horses
and asses. All that we can do with a fossil bone or
tooth is to assign it to any known species which it re-
* TJie Variation of Animals and Plants under Domestication,
vol. i. chap. ii. (1868).
ITS NEAREST EXISTING RELATIONS. 79
sembles so closely that no actual, definable difference
between them can be detected. In this sense we
may speak of Equus caballus having existed in Amer-
ica before its introduction by the Spaniards, although
it is commonly supposed that at the time of the con-
quest no horses, either wild or domesticated, were to
be found on the continent .* This is the more re-
markable as, when imported from Europe, the horses
that ran wild proved by their rapid multiplication
in the plains of South America and Texas that the
climate, food, and other circumstances were highly
favorable to their existence. The former great
abundance of Equidce in America, their extinction,
and their perfect acclimatization when reintroduced
by man, form curious but as yet unsolved problems
in geographical distribution.
In Europe, wild horses were extremely abundant
in the Neolithic, or polished-stone period. Judging
by the quantity of their remains found associated
with those of the men of that time, the chase of these
* The usual statement as to the complete extinction of the
horse in America is thus qualified, as there is a possibility of
the animal having still existed, in a wild state, in some parts
of the continent remote from that which was first visited by
the Spaniards, where they were certainly unknown. It has
been suggested that the horses which were found by Cabot in
La Plata in 1530 cannot have been introduced. See M. Wilck-
ens's "Forschungen auf dem Gebiete der Pal&ontologie der
Hausthiere" (Biolog. Centralblat,, 1889),
80 THE HORSE.
animals must have been one of their chief occupa-
tions, and they must have furnished one of their
most important food-supplies. The characters of
the bones preserved, and certain rude but graphic
representations carved on bones or reindeer's antlers
found in several caves in the south of France, enable
us to know that they were rather small in size and
heavy in build, with large heads and rough, shaggy
manes and tails — much like, in fact, the present
wild horses of the steppes of the south of Russia.
These horses were domesticated by the inhabitants
of Europe before the dawn of history. Caesar
found the Ancient Britons and the Germans using
war-chariots drawn by horses. It is, however, doubt-
ful whether the majority of the horses existing
now are derived directly from the indigenous wild
horses of Western Europe, it being more probable
that they are the descendants of horses imported
through Greece and Italy from Asia, derived from
a still earlier domestication, followed by gradual
improvement through long-continued attention be-
stowed upon their breeding and training. Such an
importation of horses from the East, for the purpose
of improving the races of Europe, has taken place at
various intervals throughout the whole of the historic
period. The most ancient monumental records of
Egypt give no sign of the existence of the horse in
ITS NEAREST EXISTING RELATIONS. 81
that country ; but about 1900 B.C. (long after the
introduction of the ass) it begins to appear, there, as
elsewhere, being first employed in drawing chariots
used in war and processions. It was not till a com-
paratively recent period that the horse was used in
agriculture, the ox being almost universally employed
in ploughing till the Middle Ages. The representa-
tion in the Bayeux tapestry of a horse drawing a
harrow is said to be the earliest indication of the
kind, and quite exceptional at that period.
Horses are now diffused, by the agency of man,
throughout almost the whole of the inhabited parts
of the globe, and the great modifications they have
undergone, in consequence of domestication and se-
lective breeding, are well exemplified by comparing
such extremes as the Shetland pony, dwarfed by
uncongenial climate and scanty food, the thorough-
bred race-horse, and the gigantic London dray-horse.
The smallest specimens of the former may be not
more than half the height of the largest of the latter*
* Mr. R. Brydon, writing in the Journal of the Royal Ag-
ricultural Society of England, 3d series, vol. i. part 1 (1890),
says: " Having measured many hundreds of them [Shetland
ponies], I am convinced that ten hands is the average height,
and that very few are found outside a range of from 9.2 to
10.2. An occasional specimen is met with as low as 8.2 when
full grown, but anything under nine hands is extremely rare,
and the largest of the pure breed rarely exceed 11 hands." On
the other hand, cart-horses between 17 and 18 hands in height
are not uncommon.
82 THE HOESE.
Perhaps the most striking instance, as it has the
certainty of a mathematical demonstration, which
can be given of the change of constitution and capa-
bility brought about by careful selective breeding in
a comparatively short space of time, is seen in the
steady progress that has been made in improving the
pace of the American fast-trotting horse. Between
1818, when records began to be systematically kept,
and 1885, the time for a mile heat has been gradually
improved from three minutes (the fastest ever ac-
complished at the former date, and which previously
was not thought possible) to two minutes, eight sec-
onds and three-quarters, which was attained on July
30 of the last-named year. Although this is at pres-
ent the highest record, past experience renders it prob-
able that it is not the greatest speed ultimately attain-
able. As bearing upon an important biological prob-
lem, much discussed at the present time, it would be
extremely interesting to ascertain, if it were possible
to do so, whether tins result has been acquired solely
by breeding from the fastest animals, and so taking
advantage of any, even the slightest, variation which
occurs in this direction in order to perpetuate the
quality in the race j or whether the careful training
that the parents have had has been capable of pro-
ducing a direct influence upon the offspring. The
first case would be an illustration of the effects of
ITS NEAKEST EXISTING EELATIONS. 83
pure selection (" artificial " in this instance, but com-
ing under the same category of causes of modifica-
tion as the " natural selection " of Darwin and Wal-
lace), the latter, of inheritance of characters acquired
during life, the potency of which has been much
called in question of late.
In Australia, as in America, horses imported by
the European settlers have escaped into the unre-
claimed lands and multiplied to a prodigious extent,
roaming in vast herds over the plains where no
hoofed animal ever trod before.
The nearest approach to truly wild horses exist-
ing at present are the so-called Tarpans, which oc-
cur in the steppe-country north of the Sea of Azoff,
between the river Dnieper and the Caspian. They
are described as being of small size, dun color, with
short mane and rounded, obtuse nose. There is
no evidence to prove whether they are really wild
— that is, descendants of animals which have never
been domesticated — or feral — that is, descended from
animals which have escaped from captivity, like the
horses that roam over the plains of America and
Australia, and the wild boars that now inhabit the
forests of New Zealand.
Darwin infers that, aboriginally, the horse must
have inhabited countries annually covered with snow,
for he long retains the instinct of scraping it away
84 THE HOUSE.
with his fore-feet to get at the herbage beneath.
Cattle, on the other hand, not having this instinct,
perish when left to themselves when the ground is
long covered with snow.
Equus przewalsMi, Poliakof . — Much interest, not
yet thoroughly satisfied, has been excited among
zoologists by the announcement (in 1881) by M.
Poliakof of the discovery by the late distinguished
Russian explorer, Prejevalsky, of a distinct species
of wild horse.* One specimen, unfortunately, only
was obtained, while searching for wild camels in
the sandy desert of Central Asia near Zaisan. It
is described as being so intermediate in character
between the equine and the asinine group of Equidce
that it completely breaks down the generic distinc-
tion which some zoologists have thought fit to estab-
lish between them. It has callosities on all four
liinbs, as in the horse, but only the lower half of the
tail is covered with long hairs, as in the ass. The gen-
eral color is dun, with a yellowish tinge on the back,
becoming lighter towards the flanks and almost white
under the belly, and there is no dark dorsal stripe.
The mane is dark brown, short, and erect, and there
is no forelock. The hah is long and wavy on the
* Proc. Imp. Russian Geographical Society, 1881, pp. 1-20,
translated by C. Delmar Morgan, in Ann. Mag. Nat. Hist. (5)
viii. pp. 16-26 (1881).
ITS NEAKEST EXISTING RELATIONS. 85
head, cheeks, and jaws. The skull and the hoofs
are described as being more like those of the horse
than the ass.
Until more specimens are obtained it is difficult to
form a definite opinion as to the validity of this spe-
cies, or to resist the suspicion that it may not be an
accidental hybrid between the kiang and the horse. *
Wild Asses. — The remaining existing species of
Equidce belong to the asinine group as defined above,
and may be conveniently divided into the plain-col-
ored, or true asses, and the striped, or zebras.
The extensive open plains of various parts of
Asia, from Syria in the west, through Persia, Afghan-
istan, the north-west of India, and the highlands of
Tartary and Thibet from the shores of the Caspian
to the frontiers of China, are the home of numerous
herds of wild asses, the individuals in each of which
may be from a dozen to twenty in number, or
amount to thousands, as described by Dr. Aitchison
in his report on the zoological results of the Afghan
Frontier Expedition of 1884. They present such a
* The brothers Grijimailo, in a paper published last year
in the Isvestija of the Russian Geographical Society (of which
a translation will shortly appear in the Proceedings of the
Royal Geographical Society of London), mention meeting with
this wild horse in the desert of Dzungaria, and are said to
have secured four skins and a skeleton of the species, a full
description of which, it may be hoped, will shortly be forth-
coming.
86 THE HOKSE.
general resemblance to each other — being all of a
uniform yellowish or isabelline color, lighter or white
below, and all having a dark brown stripe along the
middle of the back, and usually no cross-stripe on
the shoulders — that it is considered by many natu-
ralists that they should all be regarded as belonging
to one species — Equus hemionus of Pallas. There are,
however, such marked differences in size, form, and
shade of color, that they may be easily divided into
three local varieties, or races, which have been de-
scribed and named as distinct species. The true
Equus hemionus, the kiang or dzeggetai, is the largest
and the darkest in color, being of a rufous bay, and
more approaches the horse in general appearance.
It inhabits the high table-lands of Thibet, where it is
usually met with at an elevation of 15,000 feet and up-
wards. Smaller, and paler in color, being sometimes
almost silvery- white, is the onager (E. onager, Pall.),
from Persia, the Punjab, Scinde, and the Desert of
Cutch. Differing but slightly, if at all, from this, is
the Syrian wild ass, described by Geoffroy under the
name of Equus hemippus. These three all closely re-
semble each other in their habits, and are all remark-
ably swift of foot, having been known to outstrip
the fleetest horse in speed. None of them have ever
been domesticated.
The origin of the domestic ass (Equus asinus,
ITS NEAREST EXISTING RELATIONS.
87
Linn.), which, is nearly as widely diffused and use-
ful to man as the horse, was for long a matter of
uncertainty. It was known and used in Egypt long
before the horse, and the general belief that it was
Fig. 11. — African Wild Ass (Equas asinus) and foal.
From a photograph by Major J. F. Nott of animals living in the Zoological
Society's Gardens.
first domesticated in that land has been confirmed
by the discovery of a wild ass in Abyssinia and other
parts of the districts of north-eastern Africa lying
between the Nile and the Red Sea which so closely
88 THE HOUSE.
resembles certain breeds of the well-known domestic
animal as to leave little donbt as to their identity.
This has been called JEqiius tceniopus (band or stripe-
footed) by Heuglin, on account of the frequent pres-
ence of black; transverse markings upon the lower
parts of its limbs. If its identity with E. asinus
is admitted, the former name will no longer be re-
quired. It differs from the Asiatic species in being of
a more pure gray and less rufous or yellowish color,
and especially in the presence of a more or less dis-
tinct vertical, black mark (sometimes faint and nar-
row) on the shoulder, corresponding to the stripe so
constantly seen in the common domestic animals.
Its ears are also of greater length than in the Asi-
atic species of wild ass. Sir Samuel Baker says:
" Those who have seen donkeys only in their civil-
ized state have no conception of the beauty of the
wild or original animal. It is the perfection of activ-
ity and courage, and has a high-bred tone in its de-
portment, a high-actioned step when it trots freely
over the rocks and sand, with the speed of a horse
when it gallops over the boundless desert."
As with most other animals of the group, its flesh
is eaten and much appreciated by the natives of the
countries in which it lives. The bray of the Abys-
sinian wild ass is the same as that so characteristic
of the domestic variety, and the marked aversion of
ITS NEAKEST EXISTING KELATIONS. 89
the latter to cross the smallest streamlet — an aver-
sion which it shares with the camel — and the evident
delight with which it rolls itself in the dust, seem to
point to arid deserts as its original home.
The Domestic Ass is too well known to require
description. Although the variations produced by
differences of climate, treatment, and breeding are
not so great as they are in the horse, they are still
considerable, and, if careful selection and improve-
ment had been more attended to, would certainly be
far greater. As it is, the continued neglect and ill-
treatment to which this unfortunate animal has been
too often subjected, as being essentially the servant,
or, rather, the slave of the poor man all over the
world, has led to deterioration both of its physical
qualities and character.
Though gray is the prevailing color of this
species, many varieties of that color occur, and in-
stances of every shade between it and pure white on
the one hand, and dark brown or black on the other,
are met with. The dark, vertical stripe on the shoul-
der varies much in breadth and intensity of color-
ing : sometimes it is double, and not infrequently al-
together absent. The median dorsal stripe is usually
conspicuous. In size, also, there are great differences,
the asses used by the lowest caste people of the north
of India being scarcely larger than a Newfoundland
90 THE HORSE.
dog ; and in Southern Europe, especially Spain, Italy,
and Malta, they are greatly superior ; while careful
selective breeding in Kentucky has raised their height
to 15 or even 16 hands. These large varieties are
chiefly in request for the purpose of breeding mules.
The milk of the ass, containing more sugar and less
caseine than that of the cow, has long been valued
as a nutritious diet for persons of weak digestion.
Mounteney Jephson says there are great herds of
donkeys in a district to the east of the Dinka country,
which the natives only use for milking, and not as
beasts of burden.*
The ass, unlike the wild horse, is not indigenous
in Europe. In England, there is evidence of its
presence so early as the reign of the Saxon Ethelred,
but it does not appear to have been common till
after the time of Queen Elizabeth.
Striped Members of the Asinine Group of
Equhxe. — These are all inhabitants of the continent
of Africa. The animal of this group which was first
known to Europeans, and was formerly considered
the most common, is the true zebra (Equus zebra,
Linn.), sometimes called the mountain zebra. It in-
habits the mountainous region of Cape Colony, but
now, owing to the advances of civilized man into its
somewhat restricted range, it has become very scarce,
* Emin Pasha and the Rebellion at the Equator, 1890, p. 96.
ITS NEAREST EXISTING RELATIONS.
91
and is at present limited to a narrow tract near the
northern frontier of the colony. A second species,
BurchelTs zebra (Equus burclielli, Gray), still roams
in large herds over the plains to the north of the
Orange River, but in yearly-diminishing numbers.
"■"'?•*.
Fig. 12. — Common or Mountain Zebra {Equus zebra).
From a photoglyph by Mr. Gambler Bolton of an animal living in the
Zoological Society's Gardens.
Both species are subject to considerable individual
variations in marking, but the following are the prin-
cipal characters by which they can be distinguished.
Equus zebra is the smaller of the two (about four
feet high at the shoulders), and has longer ears, a
xail more scantily clothed with hair, and a shorter
92 THE HOESE.
mane. The general ground-color is white, and the
stripes are black ; the lower part of the face is bright
brown. With the exception of the abdomen and
the inside of the thighs, the whole of the surface is
covered with stripes, the legs having narrow, trans-
verse bars reaching quite to the hoofs, and the base
of the tail being also barred. The outside of the
ears have a white tip, and a broad, black mark occu-
pying the greater part of the surface, but are white
at the base. Perhaps the most constant and obvious
distinction between this species and the next is the
arrangement of the stripes on the hinder part of the
back, where there are a number of short, transverse
bands passing between the median longitudinal, dor-
sal stripe and the uppermost of the broad stripes
which pass obliquely across the haunch from the
flanks towards the root of the tail. There is often
a median longitudinal stripe under the chest.
JEquus burchelli is a rather larger and more ro-
bust animal, with smaller ears, a longer mane, and
fuller tail. The general ground-color of the body
is pale yellowish brown, the limbs nearly white, the
stripes dark brown or black. In the typical form
the stripes do not extend on to the limbs or tail ; but
there is great variation in this respect, even in ani-
mals of the same herd, some being striped quite
down to the hoofs, as shown in the specimen figured
ITS NEAEEST EXISTING RELATIONS.
93
(this form has been named E. chapmani). There is
a strongly-marked median longitudinal ventral black
stripe, to which the lower ends of the transverse side
stripes are usually united ; but the dorsal stripe (also
i
Fig. 13. — Burchell's Zebra (Equus burchelli).
From a photograph by Mr. Gambler Bolton of an animal living in the
Zoological Society's Gardens. The legs are more striped than is usual
in this species.
strongly marked) is completely isolated in its poste-
rior half, and the uppermost of the broad haunch
stripes runs nearly parallel to it. A much larger
proportion of the ear is white than in the other
species. In the middle of the wide intervals of the
94 THE HORSE.
broad black stripes of the flanks and haunches fainter
stripes are generally to be seen.
This animal is generally spoken of as the
" quagga " by colonists and hunters, but it must
not be confounded with the species to be described
under that name presently. Its flesh is greatly rel-
ished by the natives as food, and its hide is very
valuable as leather. By far the greater proportion
of zebras exhibited in European zoological gardens
and menageries at the present time belong to this
species, and it is frequently bred in confinement, and
the attempts made to break it in, and train it for
riding and driving, have been attended with partial
success.
In 1882 a living zebra was sent from Shoa, a
country lying to the south of Abyssinia, to the then
President of the French Republic, who deposited it
in the Jardin des Plantes, and, being obviously dif-
ferent from any that had hitherto been seen in Eu-
rope, it was named by M. Milne-Edwards Equus
grevyi, in compliment to his political chief. On a
white ground-color, it is very finely marked all over
with numerous delicate, intensely black stripes, ar-
ranged in a pattern quite different from those of the
other species. In view of the great variability of the
markings of these animals, as long as but one indi-
vidual of this form was known some doubts were
ITS NEAREST EXISTING RELATIONS. 95
expressed as to whether it might not be an exception-
ally-colored individual of one of the other species;
but subsequently other specimens, presenting almost
exactly the same characters, have been received from
Somali-land,* and it seems probable that all the
zebras which we know to exist in the northern
districts of East Africa belong to this species. The
very recent discovery of such a remarkable form of
animal, and the imperfect knowledge we possess of
its geographical distribution, is a striking illustration
of how much still remains to be done before we can
consider our information is complete regarding even
some of the larger and most conspicuous forms of
animal life.
Though zebras have not been found depicted on
the Egyptian monuments, they were known to the
Romans, and occasionally exhibited in the amphithea-
ters, under the name of " hippotigrisP Dion Cassius
reports that Caracalla exhibited in the circus an ele-
phant, a rhinoceros, a lion, and a hippotigris j and
as many as twenty are stated to have been collected
for the triumph of Gordian the Third, and exhibited
by his murderer and successor, Philip the Arabian
(a.d. 244).
The Quagga, or Couagga (Equus quagga, Gmelin),
* See Sclater, Proceedings of the Zoological Society of Lon-
don, 1890, p. 413.
96
THE HORSE.
is another modification of the zebra group. The
color of the head, neck, and upper parts of the body
is reddish-brown, irregularly banded and marked
with dark brown stripes, stronger on the head and
neck, and gradually becoming fainter, until lost on
the flanks, the haunches and hind quarters being
:yyS»uf
*£&$*"*
Fig. 14. — Quagga (Equus quagga).
From a photograph by Mr. York of an animal which lived in the gardens of
the Zoological Society of London, 1851-72.
quite free of stripes. There is a broad, dark, median
dorsal stripe. The under surface of the body, the
legs, and tail, are nearly white, without stripes. The
crest is very high, surmounted by a standing mane,
banded alternately brown and white. Though never
really domesticated, quaggas have occasionally been
ITS NEAKEST EXISTING KELATIONS. 97
trained to harness. A pair were driven in Hyde
Park, by Mr. Sheriff Parkins, in the early part of
the present century. The name is an imitation of
the shrill barking neigh of the animal — "ouag-ga,
ouag-ga," the last syllable very mnch prolonged.
There can be little doubt but that, owing to the
great improvements in the precision and range of
fire-arms, and the general extension of their use into
countries where till lately they were unknown, all
wild animals which yield any production of value
to man, or offer temptations to the sportsman, espe-
cially those whose geographical distribution is lim-
ited, will soon cease to exist upon the earth. The
American bison is one of the most conspicuous
instances of rapid extermination of an animal
which flourished but very recently in vast num-
bers, and which, but for the causes just mentioned,
might in all probability have continued to exist for
long ages. The various species of the large game
of Africa are quickly following in the same course.
The quagga, although described by Harris in 1839
as existing in " immense herds," is already nearly, if
not quite, extinct, the value of its hide being the
prime cause of its destruction. Regarding its for-
mer geographical distribution, Mr. H. A. Bryden
makes the following interesting remarks : " The
range of the true quagga was even more arbitrarily
98 THE HOESE.
defined. This animal, formerly so abundant upon
the far-spreading karroos of the Cape Colony and
the plains of the Orange Free State, appears never
to have been met with north of the Vaal River. Its
actual habitat may be precisely defined as within
Cape Colony, the Orange Free State, and part of
Griqnaland West. I do not find that it ever ex-
tended to Namaqnaland and the Kalahari Desert to
the west, or beyond the Kei River, the ancient eastern
limit of Cape Colony, to the east. In many conn-
tries, and in Southern Africa in particular, nothing
is more singular than the freaks of geographical dis-
tribution of animals. A river, or a desert, or a little
belt of sand or timber — none of which, of themselves,
could naturally oppose a complete obstacle to the
animal's range — is yet found limiting thus arbitrarily
the habitat of a species." *
There are thus at least seven modifications of the
horse type, at present or very recently existing, suf-
ficiently distinct to be reckoned as species by all zo-
ologists, and easily recognized by their external char-
acters. They are, however, all so closely allied that
each will, at least in a state of captivity, cross with
perfect freedom with any of the others. Cases of
* Kloof and Karroo {Sport, Legend, and Natural History
in Cape Colony, 1889).
ITS NEAKEST EXISTING EELATIONS. 99
half-breeds are recorded between the horse and the
quagga, the horse and BurchelTs zebra, the horse
and the hemionns or Asiatic wild ass, the common
ass and the zebra, the common ass and BnrchelTs
zebra, the common ass and the hemionns, the hemi-
onus and the zebra, the hemionns and BurchelPs ze-
bra. The two species which are, perhaps, the furthest
removed in general structure — the horse and the ass
— produce, as is well known, mules, which, in some
qualities useful to man, excel both their progenitors,
and in some countries, and for certain kinds of work,
are in greater requisition than either. Although oc-
casional instances have been recorded of female mules
breeding with the males of one or other of the pure
species, it is doubtful if any case has occurred of their
breeding inter se, although the opportunities of doing
so must have been great, as mules have been reared
in immense numbers for several thousands of years.
"We may therefore consider it settled that the different
species of the group are now in that degree of physio-
logical differentiation which still enables them to pro-
duce offspring with each other, but does not permit
the progeny to continue the race^ at all events unless
reinforced by the aid of one of the pure forms.
The several members of the group show mental
differences quite as striking as those exhibited by their
external form, and more than, perhaps, might be
: rzz hilsz.
r ted from the ami! ify of their cerebral organ-
ization. The patience : the bee Qm high, spirit of
■'„- "_ rs- " - - :>f the mule, have long I
•-■. iaL It is -ry remarkable that rat : -
ay g ies -hould have shown any apti-
: i _ and tl. ~ ~„ — i should
bare een from time immemorial the universal and
most : 1 mpanions and servants of mam while
all the others remain in their native freedom to this
El . - fa - . ~m a question whether this
zrom a different mental constitution,
-ing a natural capacity f i ing into relations
with m d r it may not be owing to their
:ght gradually into this condition
by long-continued and j ing efforts, when the
: i was keenly felt. It is quite
reason why nearly all of the at-
f our domestic
aTnmft1> in modern ti .led in failur
t it does not an to do so in sases in which
ipply all the principal purr
:night be put. It can hardly be
and f ggas fresh from their
native mountains and plains can be brought into
. n as beasts t burden and draught with
horses and asses, whose naturally useful qualities
have been s .^aining of thousands
ITS NEAEEST EXISTING RELATIONS. 101
of generations of progenitors. It must be remem-
bered also, that the original habitat of both the last-
named species probably lay in those conntries in
which hnman civilization took its rise, and that they
would therefore naturally be the first to be brought
beneath its influence.
CHAPTER III.
THE STRUCTURE OF THE HORSE, CHIEFLY AS BEARING
UPON ITS MODE OF LIFE, ITS EVOLUTION, AND ITS
RELATION TO OTHER ANIMAL FORMS.
THE HEAD AND NECK.
The skull — The teeth : their number ; general characters and
structure ; crown, root, pulp, dentine, enamel, and ce-
ment— Succession of teeth — Temporary and permanent
sets — Special characters of the teeth of the horse — In-
cisors— Canines — Diastema — Molars — Brachydont and
hypsodont dentition — Temporary, or milk-teeth — Time of
appearance and order of succession of the teeth — The lips
— The nostrils — The false nostrils — The guttural pouches
— The neck — Vertebras — Cervical ligament.
Next to the body of man, there is none of which
the anatomy has been more thoroughly worked out
and more minutely described than that of the horse.
It is, in fact, the one other animal body that is made
the regular subject of dissection by a whole profes-
sion of students, and to which numerous special
treatises are devoted. Monographs on its structure,
many of them copiously and beautifully illustrated,
THE HEAD AND NECK. 103
abound in most languages of the civilized world.* It
might, therefore, seem almost superfluous to add any-
thing further to the subject — certainly difficult to
say anything new.
The topographical anatomy of the horse has,
however, been always hitherto described just as if it
were a complex piece of machinery, isolated and dis-
tinct from anything else in the world, the very names
given to the parts of which it is composed often
having relation only to their conditions of existence
in the horse, and being entirely different from those
in use for the corresponding parts of man or of other
animals. Until lately, at least, the idea that the
* Among the most important of these are :
G. Stubbs : Anatomy of the Horse, 1766.
W. Percivall : The Anatomy of the Horse, 1832.
E. F. Gurlt : Anatomische Abbildungen der Haussdugethicre,
1821 ; and Handbuch der vergleich. Anat. der Haussdugethiere,
1822.
A. G. T. Leisering: Atlas der Anatomic des Pferdes, 1861.
Leisering and Miiller : Handbuch der vergleichenden AnaU
omie der Haussdugethicre, 6th edit., 1885.
Chauveau and Arloing: Traite cVanatomie comparee des
animeaux domestiques, 1871 j and English edition by G. Flem-
ing, 1873.
M. S. Arloing: Organisation du pied chcz le cheval (Ann.
Sci, Nat, 1867).
Franz Miiller: Lehrbuch der Anatomie des Pferdes, 1853.
Cuyer and Alix : Le Cheval, 1886.
J. McFadyean : Anatomy of the Horse : a Dissection Guide}
1884.
W. Youatt : The Horse, 1831.
8
104 THE STRUCTURE OF THE HORSE.
peculiarities of the horse's structure are all modifica-
tions of a more generalized form, and that their sig-
nificance can only be understood after a wide study
of the anatomy of allied forms, has never entered
into the mind of any veterinary anatomist. Cer-
tainly, in some of the most recent works, such as
that of Chauveau, attempts to harmonize the nomen-
clature of parts with that used elsewhere show a
recognition of the community of structure and origin
between the horse and other animals ; but still the
knowledge imparted in them has been more adapted
to the technical requirements of the practitioner than
to the enlightenment of those who wish for a broader
and more philosophical view of the ways of nature.
It is only proposed here to select a few of the
most leading parts, which may be of general interest,
and to show their signification and relation, describ-
ing them, as far as possible, in language which can
be understood by those who are not professional
anatomists.
For convenience the subject may be divided ac-
cording to the regions of the body in which the parts
spoken of are placed, certain of those situated in
the head and neck being first selected for considera-
tion ; while the limbs, which are of as great impor-
tance philosophically as they are practically, will be
reserved for another chapter.
THE HEAD AND NECK. 105
The Skull.
The general form of the head of the horse is de-
termined by that of the skull, which forms its sup-
porting framework, and which is of very peculiar
and characteristic shape. As in other animals, it is
composed of two main portions : (1) the cranium, or
skull proper, consisting of a great number of bones,
originally quite distinct, but which are eventually
firmly united so as to form a solid mass ;* and (2)
the mandible, or lower jaw, fastened to the former
by a freely movable hinge-joint.
The cranium is movably joined to the front end
of the vertebral column by means of a pair of oval
eminences called " condyles," which fit into corre-
sponding cavities in the atlas, or first vertebra of the
neck. Between these condyles is a large opening
{foramen magnum), through which passes out of the
cranium the spinal cord, or backward prolongation
of the central nervous system, which is expanded in
the head to form the brain.
The cranium may be roughly divided into two
portions — a hinder part, or brain-ease, consisting of
a solid bony capsule for inclosing and protecting
* The outlines of the individual bones are perfectly well
marked in young subjects, being indicated by fine dividing-
lines, called sutures. In old age these often become more or
less obliterated by the union of the contiguous bones.
106 THE STRUCTURE OF THE HORSE.
the brain j and a facial part, for the support of the
organs of sight, taste, and smell, and of those con-
cerned in seizing and masticating the food.
The skull of a man (Fig. 15) and the skull of a
horse (Fig. 16) are composed of exactly the same
number of bones, having the same general arrange-
ment and relation to each other. Not only the in-
dividual bones, but every ridge and surface for the
attachment of muscles, and every hole for the pas-
sage of artery or nerve, seen in the one can be traced
in the other. Yet they differ remarkably in general
aspect. The difference mainly lies in this : in man
the brain-case is very large and the face of relatively
minute proportions. In the horse, on the other hand,
the brain is extremely reduced, and the face, espe-
cially the mouth, of enormous size. In other words,
the characteristic form of man's head is chiefly due
to his great brain, that of the horse to the compara-
tively large development of the apparatus for mas-
ticating his food.
Taking the different regions of the horse's skull
(Fig. 16) into closer consideration, and beginning at
the hinder, or " occipital " en$, we may observe the
rounded, almost polished surface of the condyles (oc),
already mentioned, which, fitting accurately into the
corresponding depressions of the atlas, and in life
covered with a soft, perfectly smooth layer of carti-
THE HEAD AND NECK.
107
lage and lubricated with synovial fluid, allow the
head to move freely up and down, or sideways, even
Fig. 15. — Side view of the skull of man, with the
bone removed so as to show the whole of the teeth.
z, zygomatic arch ; n, nasal bone ; o, or it ; t, tem-
poral fossa ; oc, occipital condyle ; e, external audi-
tory opening; g, glenoid fossa for articulation of
the lower jaw ; c, coronoid process of lower jaw ;
i1 and i~, incisor teeth; ceo, canine; pm1 andjw*2,
premolar teeth; m1, m2, and m?, the three molar
teeth.
when the neck is fixed. The same region also shows
various roughened, projecting ridges or promontories
for the attachment of the powerful ligaments and
108 THE STRUCTURE OF THE HORSE.
muscles required to support and move so heavy a
head, projecting forwards at the end of so long a
neck. Above, on each side, are the " occipital crests,"
joining in the middle line to form the " occipital pro-
tuberance," to which that remarkable structure, the
"nuchal," or " cervical ligament," to be spoken of
further on, is attached. On each side a large, wing-
like process (par-occipital) # descends, for the attach-
ment of the great lateral muscles of the neck. The
head of man, nicely balanced on the top of the verte-
bral column, does not require any such great devel-
opment of these parts, and they are, consequently, in
a quite rudimentary condition in him.
On the lateral surface of the skull, the opening
(em) which leads to the internal ear, or true organ
of hearing (embedded in the bones which form the
side wall of the brain-case), will be seen, to the
roughened margin of which the base of the cartilag-
inous " pinna," or projecting external ear, is attached.
Although we commonly speak of this latter as the
" ear," as it is the only externally visible part of the
complicated organ by which sounds are recognized,
it is a mere accessory, the use of which is to aid in
collecting the vibrations passing through the air,
* This is the " styloid process " of veterinary anatomy,
but not to be confounded with the parts bearing the same
name in human anatomy.
THE HEAD AND NECK.
109
and direct them towards the internal, delicate, and
beautifully-constructed apparatus in which, by their
oc.
Fig. 16.— Side view of the skull of horse, with the
bone removed so as to show the ^hole of the
teeth, n, nasal "bone ; o, orbit ; z, zygomatic arch ;
t, temporal fossa ; oc, occipital condyle ; em, exter-
nal auditory opening ; g, glenoid fossa for articula-
tion of the lower jaw; »', il, i%, the three incisor
teeth ; c, the canine ; pm1, the situation of the ru-
dimentary first premolar, which has been lost in
the lower, but is present in the upper jaw ; pm*,
pmz, and pm4, the three fully-developed premolar
teeth ; m\ m?, and m3, the three true molar teeth.
effects upon the terminations of the auditory nerve,
they produce the sensation of hearing.
In front of the ear-opening arises a curious bridge
of bone (z), which arches forwards to join the skull
110 THE STKUCTUKE OF THE HOESE.
again at the hinder part of the face. This is called
the " zygomatic arch," and is almost constantly pres-
ent in the skulls of mammals.
Standing out as it does, it allows the npper part
of the under jaw to work beneath it, and its onter
surface affords a very advantageous point of attach-
ment to a great muscle (masseter), to be spoken of
presently. The side of the brain-case between this
and the top ridge of the sknll is called the " tempo-
ral fossa" (t). Though bounded by raised ridges all
round, enough to give it the general character of a
depression or fossa, its floor is formed by a convex
surface, the side of the actual brain-cavity. The
fossa is mainly filled in life by one of the muscles
(temporal) which close the jaw, but its anterior part
contains much fat, the loss of which in old horses
gives rise to the characteristic depression seen in
them above the eye. Farther forward is the cavity
(o)} of almost circular outline, in which the eyeball
is lodged, called the " orbit," with very sharply de-
fined and complete outer and hinder margin, formed
by a bridge of bone passing upwards from the zygo-
matic arch to join the "frontal," or forehead-bone.
This is a point in the anatomy of the horse to be es-
pecially noticed, as it gives a very characteristic ap-
pearance to his skull. The interest of this bridge of
bone, dividing the orbit from the temporal fossa, is
THE HEAD AND NECK. Ill
that it did not exist in any of the primitive Ungulates
of the Eocene period, in which, consequently, these
two cavities, or fossa?, were freely continuous (see
skull of Phenacodus in Fig. 2, p. 21). Moreover, it
does not exist in any other of the Perissodactyles of
the present time (tapir or rhinoceros), but is a spe-
cial and recently acquired character, developed only
in the later stages of the horse group, not being met
with in any of the ancestral forms until after the
close of the Miocene period.
The horse, however, is by no means alone among
mammals in possessing it ; but whenever it occurs, it
appears to be an evidence of advance in structure,
being found in the higher and more recent forms of
several groups, the lower and more ancient members
of which do not possess it. In man it has attained
its most complete development, for not only is there
a bridge, but also a wall extending inwards from it,
cutting off almost completely the two cavities from
one another.
In front of the orbit a great, flat expanse, the
" cheek," extends quite to the fore-part of the face,
giving room for the long row of -upper molar teeth,
and within, for the lodgment of the highly-devel-
oped organ of smell. This is roofed over above by
" nasal bones " (n) of great size, terminating in front
by freely-projecting, pointed, and somewhat decurved
112 THE STRUCTURE OF THE HORSE.
ends, which support the well-developed external nos-
trils. The palate, which forms the floor of all this
part of the skull, is remarkable for its great length
and comparative narrowness. The front end of the
upper jaw consists of the united " preniaxillary
bones," which expand and curve down to form the
semicircular border supporting the large incisor
teeth. In the middle line, in front, between the pre-
maxillaB below and the nasals above, is the large, ir-
regular opening of the " anterior nares," leading into
a great chamber or passage, divided into two by a
vertical median wall or septum. Through this cham-
ber the air passes in respiration to the " posterior
nares," a smaller opening at the base of the skull
behind the palate, and in the upper part of it is
placed the sponge-like mass of bones which support
the terminations of the olfactory nerves, constituting
the organ of smell. Before leaving the cranium, the
" glenoid n cavities, or, rather, surfaces (</), to which
the two branches of the mandible are articulated,
must be mentioned. They are placed just below the
hinder end of the zygomatic arch. They are wide
transversely, concave from side to side, convex from
before backwards in front and hollow behind, and
bounded posteriorly at the inner part by a promi-
nent " post-glenoid " process, which effectually pre-
vents the jaw from being dislocated backwards.
THE HEAD AND NECK. 113
The lower jaw, or "mandible/' consists of two
halves or branches ("rami"), originally distinct, but
firmly nnited in adult horses by their front ends (the
symphysis). Each is articulated to the correspond-
ing glenoid surface of the cranium by its " condyle/'
placed at the hinder and upper end of the ramus. The
smooth, articular surface of this is very wide trans-
versely, but narrow and convex from before back-
wards. The principal action at this joint is that of
a simple hinge, but the form of the contiguous sur-
faces allows a certain amount of motion in other
directions, far more, for instance, than is permitted
in the very -complete interlocking hinge- joint of the
Carnivora.
In front of the condyle, and separated from it by
a notch, rises a somewhat small and slender, back-
ward-curving "coronoid process'7 (co, Fig. 15), for
the attachment of the temporal muscle, which aids in
closing the jaw. Below it is a flat, broad, expanded
surface, reaching down to the "angle" (where the
horizontal and vertical or ascending portions of the
jawbone meet), for the attachment of the huge mas-
seter muscle, arising from the zygomatic arch, and
from a well-marked ridge running horizontally for-
wards on the cheek in continuation of the lower bor-
der of the arch. This muscle is the main agent in
closing the mouth, and therefore in crushing the
114 THE STRUCTURE OF THE HORSE.
food between the molar teeth. The horizontal por-
tion of the jaw, long, straight, and flattened from side
to side, carries the great molar teeth, and gradually
narrows towards the symphysis, where it expands
laterally, to form, with the united opposite ramus,
the wide, semicircular, shallow alveolar border for
the lower incisor teeth.
The Teeth.
The next parts to which attention may be called
are the teeth, which in the horse, though founded
upon the same general type as the primitive Ungu-
lates of the Eocene period, have undergone a remark-
able amount of specialization, fitting them in an
eminent degree for the purpose they have to fulfill.
Number of the Teeth. — For convenience of descrip-
tion teeth are divided, according to their situation in
the mouth and other characters, into four sets, called
(beginning from the front) incisors, canines, premo-
lars, and molars. As mentioned in the first chapter,
all the early Ungulate mammals, without exception,
had on each side, above and below, three incisors,
one canine, four premolars, and three molars — that
is, eleven on each side above, and eleven below, or
forty-four altogether. The modern horse has nearly,
if not quite, this full number. The front teeth, or
incisors, are the same — six above and six below, tak-
THE HEAD AND NECK. 115
ing the two sides together (Fig. 16, i\ i\ and i3). The
canines, or " tnshes " (c), are present, as a rule, only
in the males. The cheek-teeth (pm2 to m3), or pre-
molars and molars taken together (for there is very
little to distinguish them in form or size), are gener-
ally but six, instead of seven, on each side above
and below. Here, then, is a case of specialization by
suppression. One of the teeth of the ancient forms
has disappeared. Which is it? The examination
of a series of fossil remains shows us that the first
of the series — the anterior premolar {pm1), a fairly
large and well-developed tooth in Phenacodus
and Hyracotherium — gradually became smaller and
smaller as time advanced. It is still present in An-
chitherium, sometimes present and sometimes absent
in Hipparion. But has it entirely disappeared in the
modern horse ? What do we read in old books on
veterinary surgery ? " Wolves ' teeth are two very
small, supplementary teeth, appearing in front of the
molar teeth, and supposed to have an injurious effect
on the eyes ( !), and are, therefore, often removed by
farriers."
These little rudiments of teeth, about which such
nonsense as the above has been written, are, when
properly understood, of intense interest. Their di-
minutive size, their irregular form and inconstant
presence, combined with their history in the extinct
116 THE STRUCTURE OF THE HOESE.
horse-like animals, show them to be teeth which, for
some reason to us at present unknown, have become
superfluous — have been very gradually and slowly (as
in the case of all operations of the kind) dispensed
with, and are in the stage to which the horse has now
arrived in its evolution, upon the point of disappear-
ance. The presence of these so-called " wolves'
teeth " alone is sufficient, if we had no other proof,
to show that the horse is not an isolated creation,
but one link in a great chain of organic beings. The
fact that these teeth are almost always met with in
the upper jaw only, should be noted in connection
with what has been previously mentioned respecting
the dentition of the tapir. The first upper premolar
is retained in that animal, while the corresponding
lower tooth has entirely disappeared.
It would be very interesting, if a sufficiently large
number of specimens could be examined, to obtain
some statistical imformation as to the relative fre-
quency of the occurrence of these teeth in the differ-
ent species of wild and different breeds of domestic
horses. They are usually so loosely attached in the
skull that they become lost in specimens prepared
for museums ; but indications can generally be seen
on the bone, if they have been present.
General Characters and Structure of Teeth. — Before
describing the teeth of the horse a little more in de-
THE HEAD AND NECK. 117
tail, it will be necessary to give some slight account
of the characters and structure of these organs in
general, in order that the special descriptions may
be better understood.
Every tooth may be divided into two principal
parts, a "crown," and a "root" (sometimes errone-
ously called " fang"). The part connecting the two,
often indicated by a constriction, is called the " neck."
The crown is the only part which is seen in the liv-
ing animal, the root being implanted in a socket in
the bone, just as the roots of a tree are in the ground.
The crown may be variously shaped — conical and
pointed, chisel- or awl-shaped, broad, flat, or rounded ;
or it may be complicated by the development upon its
surface of elevations or tubercles, called cusps, or by
variously disposed crests or ridges. The root may be
single, or divided into two or more conical, tapering
branches.
In structure, the teeth are composed of several
distinct substances, differing from each other in
character and degree of hardness. The most im-
portant of these are :
1. The pulp, a soft substance, abundantly supplied
with blood-vessels and nerves, constitutes the central
axis of the tooth, and affords the means by which its
vitality is preserved. This occupies a larger relative
space, and performs a more important purpose in the
118 THE STRUCTURE OF THE HORSE.
young, growing tooth than afterwards, as, by the
calcification and conversion of its outer layers, the
principal hard constituent of the tooth, the dentine,
is formed. In teeth which have ceased to grow the
pulp occupies a comparatively small space, which in
the dried tooth is caUed the pulp-cavity. This com-
municates with the external surface of the tooth by
a small aperture at the apex of the root, through
which the branches of the nutrient blood-vessels and
sensitive nerves necessary to maintain the vitality of
the tooth pass in, to be distributed to the pulp. In
growing teeth the pulp-cavity is widely open below,
while in advanced age it often becomes obliterated,
and the pulp itself entirely converted into bone-like
material.
2. The dentine, or ivory, forms the principal con-
stituent of the greater number of teeth. It is a
very hard but elastic substance, white, with a yel-
lowish, tinge, and slightly translucent. Its chemical
composition is very like that of bone, but its micro-
scopical structure is altogether different.
3. The enamel constitutes a thin investing layer,
complete or partial, of the exposed or working sur-
face of the dentine of the crown of the teeth of most
mammals. This is the hardest tissue met with in the
body, containing from 95 to 97 per cent, of mineral
substances (chiefly phosphate, and some carbonate of
THE HEAD AND NECK. 119
lime, with traces of fluoride of calcium). Enamel
is easily distinguished from dentine with the naked
eye by its clear, bluish- white, translucent appearance.
4. The cement, or Crusta petrosa, is always the
most externally placed of the tissues of which teeth
are composed. It is often only found as a thin layer
upon the surface of the root ; but sometimes, as in
the complex-crowned molar teeth of the horse and
elephant, it is a structure which plays a very impor-
tant part, covering and filling in the interstices be-
tween the ridges of the enamel. Its structure and
chemical composition is almost exactly that of ordi-
nary bone.
Succession of Teeth. — The dentition of all mam-
mals consists of a definite set of teeth, of constant
and determinate number, form, and situation, and,
with few exceptions, persisting in a functional con-
dition throughout the natural term of the animal's
life. In many species these are the only teeth
which the animal ever possesses — the set which is
first formed being permanent, or, if accidentally
lost, or decaying in extreme old age, not being re-
placed by others. But in the horse, as in all other
Ungulates, as well as in man, and, in fact, the major-
ity of the class, certain of the teeth are preceded by
others, of a smaller size, which occupy the place of
the permanent teeth during the growth and gradual
9
120 THE STRUCTURE OF THE HORSE.
maturation of the latter, and especially while the
jaws are acquiring size and strength sufficient to
support them. In all cases these teeth disappear (by
the absorption of their roots and shedding of the
crowns) before the frame of the animal has acquired
complete maturity. As the first set of teeth are, as
a general rule, present during the period in which
the animal is nourished by the milk of the mother,
the name of " milk-teeth " (French, dents de lait; Ger-
man, Milchzahne) has been commonly accorded to
them, although it must be understood that the time
of their duration has nothing to do with that of lac-
tation. "Temporary teeth," or "deciduous" teeth,
are, perhaps, therefore, better names. No mammal
has more than two sets of teeth.
Special Characters of the Teeth of the Horse. — In-
cisors. — To return to the teeth of the horse. The
incisors, or " nippers," as they are called in veterin-
ary language, of each jaw, are placed in close con-
tact, forming a semicircle. The crowns are very
large, somewhat chisel-shaped, and of nearly equal
size. They have all a peculiarity not found in any
other existing mammal,* and seen only in the
Equidce of comparatively recent geological forma-
tions. In the most primitive species these teeth
* Macraiichenia, an extinct South American Perissodac-
tyle, had somewhat similar incisors.
THE HEAD AND NECK.
121
were simple, and chisel- or awl-sliaped. When their
crowns became worn in consequence of long-contin-
ued use, they presented an external ring of enamel,
surrounding a core of the dentine, or ivory, of which
the bulk of the tooth is composed. This is the con-
dition of the incisor teeth in the great majority of
mammals. The first modification from this simple
form consisted in the development of a ridge along
the hinder border of the base of the crown, as seen
in Fig. 17. There was then a groove between this
ridge and the rest of the tooth. By the continuous
Fig. 17. — Incisor tooth
of Anehitherium au-
relianense.
Fig. 18. — Unworn crown
of temporary incisor
tooth of young horse.
increase of the ridge, and its union with the edges of
the main part of the crown on each side, the groove
became converted into a deep pit (infundibulum),
the orifice of which is transversely elongated, and
placed behind and rather below the cutting-edge of
the tooth. This is the condition seen in a colt's in-
cisor which has just cut the gum (Fig. 18). As wear
122
THE STKUCTUEE OF THE HORSE.
takes place, the surface, besides the external enamel
layer, as in the ordinary simple tooth, shows, in ad-
dition (see Fig. 19), a sec-
ond, inner ring of the same
substance surrounding the
pit, which, of course, adds
greatly to the efficiency of
the tooth as an organ for
biting tough, fibrous sub-
stances. The bottom and
sides of the pit are par-
tially lined with cement,
but a considerable cavity
remains, generally filled,
in the living animal, with
particles of food, and, be-
ing conspicuous from its
Fig. 19. -Incisor tooth of dark color> & constitutes
horse, with the crown par- the «mark» by which the
tially worn, showing the pit ^
surrounded by its enamel age of the horse is judged,
layer, outside of which is
the dentine with its external In consequence of its
enamel covering. The en- , -..
amel is represented white, 01lly extending to a Cer-
P^teblackiUe ^^ and the tain dePth ^ the Cr0Wn>
it becomes obliterated as
the tooth wears away, the section of which then as-
sumes the character of that of an ordinary incisor, con-
sisting of only a core of dentine, surrounded by an
THE HEAD AND NECK. 123
external enamel layer. The flattened, worn surface of
an incisor tooth, as seen in Fig. 19, is called, in works
of descriptive veterinary anatomy, "the table." It
is totally different in appearance from the summit of
an unworn tooth, with its thin, rounded, shell-like
margins surrounding the deep, open cavity, as in
Fig. 18 *
The permanent incisors of the horse (like the
molars, as will be explained hereafter) differ from
those of most mammals in the great length of their
crowns, which do not remain fixed in position when
they have once come into place, but continue to
push up from below, as they wear away at the ex-
posed surface, for a considerable part of the life of
the animal. The upper part of the tooth, or that
which first appears, is very wide transversely, and
narrow from before backwards ; but the form grad-
ually alters, becoming narrower from side to side,
and finally somewhat triangular in section, flat in
front, and with a projecting ridge in the middle, be-
hind. Consequently, the shape of the table alters
as the wear of the tooth proceeds, and by its form
gives indications of great assistance in determining
the age of the animal. A considerably worn table
shows, in addition to the mark caused by the pit or
* This appearance has given rise to the term of " shell "
teeth, applied to newly-cut, unworn incisors.
124 THE STRUCTURE OF THE HORSE.
infundibulum, another spot, having a cloudy-yellow
color, always situated in front of the pit when the
two coexist, and continuing, after the obliteration of
the former, quite to the base of the root, This is
caused by the pulp-cavity, which has become filled
up by an irregular deposit of dentine. As it has no
surrounding of enamel, it cannot be mistaken for
the pit, or true mark.
The three incisors of each side of the jaw, begin-
ning at the middle hue, are spoken of as "central"
or "pincers," "lateral" or "intermediate," and "cor-
ner" teeth. For brevity of description they are
symbolized as i\ P, and is.
The characters of the incisor teeth in the three
existing families of Perissodactyles offer an inter-
esting subject for consideration. All originating
in a similar, and comparatively simple form, they
have all varied from it in totally different direc-
tions. Those of the tapirs show the least change
from the primitive condition ; those of the rhinoce-
roses have dwindled down in number and size, to
complete disappearance in some species; those of
the horses have undergone changes leading, finally,
to a complication of structure unknown in any other
existing animal. There can be little doubt but that
these changes have all been in adaptation to some
peculiarities of the environment of the animals, and
THE HEAD AND NECK. 125
that each has been best adapted for the purpose
which it has had to fulfill ; but the relations between
use and structure are often of such a delicate and
intricate character that they quite escape the recog-
nition of our limited powers of observation.
The Canines. — Separated from the incisors by a
short interval are the teeth called in the general
language of zoology " canines/' but usually spoken of
in the horse as the "tusks/' or, more often, "tushes"
(Fig. 16, c). They correspond exactly with the tusks
of the boar and the great corner teeth of the lion
and dog; but in all the Equidw they play a very
subordinate part, not being required either as a
means of defense or for the purpose of seizing prey.
Following a very general rule among the Mammalia,
especially marked in the Ungulates and other groups
(as monkeys) in which these teeth are not a necessity
for procuring food, they are much more developed
in the male than in the female. Indeed, they are
practically absent in the latter sex, as, when they do
occur as an exception, they are in a more or less
rudimentary condition. As the canines were present
in both sexes in the Eocene and Miocene Ungulates,
their loss in the females of the existing Equidce must
be reckoned, like the loss of the anterior premolar,
among the numerous instances of specialization
which this group has acquired.
126 THE STRUCTURE OF THE HORSE.
It may be remarked in passing, that the canines
are the only teeth which afford indications by which
the sex of an animal may be distinguished, except,
of course, such as may be inferred from the general
disparity of size which characterizes the entire denti-
tion, in common with the rest of the organization,
in many cases.
In the adult male horse they are always present
in both upper and lower jaw, but they are smaller
than the incisors, and of different form, being, when
unworn, pointed at the apex, and presenting noth-
ing resembling the pit or infundibulum. They have
a tendency to curve, the concavity being turned back-
wards. Their outer surface is smoothly convex;
their inner surface has a prominent, rounded, lon-
gitudinal ridge, and a groove on each side. The bor-
ders separating their outer and inner surfaces are,
when unworn, sharp and cutting, and meet at the
apex.
Blastema. — Isolated as the canines are from the
incisors in front, they are separated by a still wider
interval (or " diastema ") from the molar teeth behind.
This toothless interval, called the " bar " in the lower
jaw, is of essential importance in the domesticated
horse to his master, as without it there would be no
room for the insertion of the special instrument of
subjugation to his commands — the bit. In the most
THE HEAD AND NECK. 127
primitive condition of dentition there appears to
have been no such interval, all the teeth being in
contact ; and this condition is retained, or perhaps
regained, by man, almost alone among existing
mammals. Already, in Phenacodns, there was an
indication of this diastema, and throughout the
whole series of Perissodactyles which lead np to the
Equidce there has been a gradual increase of its
length.
Molar Teeth. — The cheek-teeth, or molars, exclud-
ing the rudimentary and inconstant anterior pre-
molar, spoken of before, are six in number, above
and below, on each side (see Fig. 16, pm2 to mz).
They are all in such close contact, by broad surfaces
fitting tightly against each other, that they form to-
gether one solid mass, presenting a grinding-surface
composed of substances of various densities, and
therefore projecting at slightly different levels, inter-
woven in such an intricate pattern as to form one of
the most efficient natural millstones imaginable.
A distinction must be pointed out among these
teeth. In a great many animals their form differs
so much that they are readily -separated into an
anterior set of simple character, and a posterior set,
larger, broader, and with more complex crowns and
roots j and when it was discovered that these also
presented a constant difference in their mode of
128 THE STRUCTURE OF THE HORSE.
development — the first set being preceded in their
places by other teeth of the milk, or deciduous series,
and the last set coming up behind the last of the
milk-teeth, without any predecessors — the distinction
was thought to be of sufficient importance to give
them different names, the first being called " premo-
lars," or " false molars," and the last " true molars."
In the horse there is no difference in form or size
between the premolars and true molars, and it is only
by the analogy of other animals, and by a knowl-
edge of their early history in the horse itself, that
we can divide them, and know that the great mill-
like mass of cheek-teeth consists of three premolars
and three molars.
It is characteristic of a primitive condition of
dentition that premolars and molars should differ
in form. Such a condition is, doubtless, best adapted
for an omnivorous or generalized mode of feeding ;
but it is a specialty on the part of the Perissodactyles,
which was acquired very early in their history, and
is, no doubt, in accordance with their strictly vege-
tarian life, that the premolars have taken on the form
of the true molars, and have become as completely
adapted as the latter for the grinding function.
Another and still more important deviation which
has taken place in the general condition of the molar
teeth from their primitive state is this. The crowns
THE HEAD AND NECK. 129
of all teeth in the early forms were very low, or
short from above downwards, and therefore bnt
slightly elevated above the surface of the jaw. There
was a distinct constriction — the neck — between the
crown and the root, and when the tooth was develop-
ing, as soon as the neck once rose fairly above the
margin of the bone, the tooth remained permanently
in this position. The term " brachydont n expresses
this condition of tooth, which was universal in Peris-
sod actyles up to and including the Anchitherium of
the Miocene epoch (see a, Fig. 20). The free surface
of the crown presented cusps and ridges upon it,
with valleys between ; but the valleys were shallow,
and had no deposit of cement filling them, the whole
exposed surface of the unworn tooth being formed
of enamel. When the ridges became worn down by
the friction of hard particles of food interposed be-
tween the opposing teeth, the dentine of the interior
was exposed, forming islands surrounded by enamel.
As the wear continued and reached the bottom of
the valleys, all the enamel coating disappeared from
the upper surface, and nothing remained but a plane
surf ace of comparatively soft dentine, surrounded at
the circumference by the enamel. With the progress
of time, however, individual succeeded individual, in
each of which, probably by insensible degrees, the
crowns of the teeth became longer, the valleys deeper,
130 THE STRUCTURE OF THE HORSE.
and the ridges not only more elevated, but more
curved and complex in arrangement. To give sup-
port to these high ridges, and to save them from
breaking in use, the valleys and cavities between
them became filled up to the top with cement, which
was also packed round the whole outer surface of
the enameled crown, and as the tooth wore down the
result was an admirable grinding-surface, consisting
of patches and islands of the two softer substances
— dentine and cement — separated by variously re-
duplicated and contorted lines of intensely hard en-
amel, the greater resistance of which to the attrition
of the food caused it to project slightly above the
rest of the surface (see section of the tooth of Hip-
parion, Fig. 10, p. 71). To this lengthened form of
crown the term "hypsodont " is applied. Instead of
contracting into a neck and forming roots, its sides
continue parallel for a considerable depth in the
socket, and as the surf ace wears away the whole tooth
slowly pushes up, and maintains the grinding-edge
constantly at the same level above the alveolar bor-
der, much as in the perpetually-growing front teeth
of many rodents, which never contract at the base to
form roots, but continue throughout the life of the
animal to grow from below to the same extent as
they are worn away at the outer, or cutting-edge.
But the horses have not quite attained this condition.
THE HEAD AND NECK.
131
There is still a limit to the growth of their teeth.
After a length is attained which, under normal con-
ditions, supplies sufficient grinding-surface to last
the lifetime of the animal, a neck and roots are
formed, and the tooth is reduced to the condition
Fig. 20. — a, Lower molar of Anchitherium (brachy-
clont form) ; b, lower molar of a young horse, with
the crown slightly worn and the roots not yet
formed (hypsodont form) ; c, the same tooth of an
old horse, with the crown almost entirely worn
away and the roots fully formed.
of that of the brachydont ancestor (see h and c,
Fig. 20).
It is perfectly clear that this lengthening of the
crown adds greatly to the power of the teeth as or-
gans of mastication, and enables the animals in which
it has taken place to find their sustenance among
132 THE STRUCTURE OF THE HORSE.
the comparatively dry and harsli herbage of the
plains, the stalks of which often contain much hard
mineral matter, instead of being limited to the soft
arid succulent vegetable productions of the marshes
and forests in which the primitive brachydont forms
of Ungulates mostly dwelt.
The hypsodont, or high-crowned type of tooth,
which may be looked upon as an intermediate condi-
tion between the rooted and the ever-growing type,
is by no means peculiar to the molars of the horse.
It occurs, as already mentioned, in the incisors of
the same animal. It is also met with, in various
degrees, in the more recently-developed forms of the
rhinoceros family (though not in the tapirs), and in
some of the most specialized of the Artiodactyles, as
the ox and the sheep, though not attaining in those
animals to the same development which it does in
the horse.
As there are some differences in the details of the
structure of the premolars and molars of the upper
and lower jaws, it will be necessary to describe them
separately.
Of the six principal teeth which constitute the
upper molar series, the four middle ones (the last
two premolars, pmz and pm\ Fig. 16 ; and the first
two molars, m1 and m2) are almost exactly alike in
size, form, and structure, being, roughly speaking,
THE HEAD AND NECK.
133
four-sided prisms with a nearly square section. The
foremost, pm% and the hindermost, m% differ from
the others, being more triangular in section, the apex
of the triangle pointing forwards in the first aud
backwards in the last.
To understand properly the arrangement of the
enamel folds and of the dentine within, and the
Fig. 21. — a, grinding-surface of unworn molar tooth
of Anehitherium ; 6, corresponding surface of un
worn molar of young horse ; c, the same tooth after
it has been some time in use. In the latter, the
uncolored portions are the dentine or ivory, the
shaded parts the cement filling the cavities and sur-
rounding the exterior. The black line separating
tliese two structures is the enamel, or hardest con-
stituent of the tooth.
cement on the outside of them, as seen in a section
or in the naturally worn surface of one of the mid-
dle teeth, it is necessary to examine it in its unworn
and even unfinished state, before the thick coat of
cement has been deposited around the ridges and
projections of the surface. Such teeth can always
be found within the sockets of the prepared skulls
134 THE STRUCTURE OF THE HORSE.
of young animals, and deserve careful study, on ac-
count of the light they throw upon the structure of
the organ in its maturity. It will be seen (Fig. 21)
that the pattern presented by the free surface is es-
sentially similar to that of the corresponding tooth
of Anchitheriuni, which is itself a modification of
that of Hyracotherium, from which it is but an easy
transition to Phenacodus, as shown in the first chap-
ter. The main difference is that, in the short-crowned
tooth of Anchitherium, the ridges and valleys are nec-
essarily very shallow, with sloping walls, and there is
no need for a packing of cement around and within
them ; while in the horse they descend the whole
depth of the elongated crown of the tooth, with
nearly parallel walls, so that any part presents an
almost identical section, and they are filled in and
packed round with an abundance of cement. The
fout* original main cusps — antero-internal, postero-
internal, antero-external, and postero-external —
and also the two intermediate cusps are distinctly
recognizable, but they are prolonged anteriorly and
posteriorly into ridges or walls taking a generally
crescentic form, with the concavity of the crescent
looking outwards, and its convexity inwards. It is
this disposition which gives the outer surface of the
teeth its deeply ridged and grooved or fluted charac-
ter, the two deep grooves corresponding with the
THE HEAD AND NECK. 135
concavities of the two outer crescents. The internal
columns, especially the anterior one, have a great
tendency to detach themselves from their crescents
formed by the intermediate cusps. The amount of
detachment and the form of -this column in section
are important in determining the various species of
fossil jEquidm, and its complete detachment in the
Hipparion (Hippotherium) forms one of the principal
characters (already alluded to) by which that genus
is distinguished from the other members of the
group (see Fig. 10, p. 71).
The two deep holes, of a roughly crescentic shape,
filled with cement, are spoken of, for descriptive pur-
poses, as the anterior and posterior lakes. The sinu-
osities of their enamel margins, which are sometimes
extremely complex, present great variations in differ-
ent species, as also do the indentations in the edges
of the sinus which runs forwards from the inner side
of the tooth between the twro internal columns, the
form of the folds at the bottom of which constitutes
the only easily recognizable distinction between the
molar tooth of the common horse and the ass.
Though the length of the combined grinding-sur-
faces of the upper and lower molar teeth is practi-
cally the same, the latter are scarcely more than half
the width from side to side, and present quite a dif-
ferent pattern. As in the upper series, those placed
10
136 THE STKUCTUKE OF THE HOESE.
at either extremity narrow off anteriorly and pos-
teriorly, but the fonr middle ones are almost iden-
tical. The pattern of these teeth resembles essen-
tially that of most of the other Perissodactyles. They
consist mainly of two crescents, one placed in front
of the other, with their convexities outwards ; but it
is peculiar to the Uquidce to have the inner ends of
the crescents complicated by the addition of columns
or lobes, which add considerably to the intricacy of
the pattern exposed when the tooth is worn. The
extremely hypsodont condition and the quantity
of cement which everywhere overlays the enamel
and fills in the interstices of the foldings are also
special characters of this group, which they share
only with the Elasmotherium among the Rhinocero-
tidae.
The surfaces of the upper and lower molars in
wearing against each other do not come in contact
in a plane horizontal to the long axis of the tooth,
but in one slanting from without upwards, the wear
being greatest on the inner side of the upper teeth
and the outer side of the lower teeth.
The roots of the molars are short, and in the up-
per ones four in number, except in the first and last,
which have only three. In the lower teeth there are
two, one anterior and one posterior, in position.
After they are fully formed, the tooth does not con-
THE HEAD AND NECK. 137
tinue to grow, but gradually rises towards the sur-
face of the socket, the bottom of wThich fills up with
bone, so that in very old horses the crowns are en-
tirely worn away, and nothing but the roots of the
teeth remain, loosely implanted in the jaw. If from
any accidental cause one of the teeth is absent, the
tooth opposite to it in the other jaw, having nothing
to wear against, will gradually rise high above the
level of its fellows.
Temporary or Milk- Teeth. — The first, temporary,
deciduous, or milk set of teeth of the horse, though
on the whole resembling the permanent set, having
the characteristic enamel foldings arranged on the
same general principle, present several interesting
peculiarities.
The incisors are in number the same as . the per-
manent teeth of this class. They are, however, not
only smaller, but, as they are only required to be in
use for a limited time, they have not need of the
lengthened crowns passing indefinitely into the root
possessed by the latter, and therefore show distinctly
the broad crown, contracted neck, and definite root
of the brachydont type of tooth. In this respect
they resemble the ancestral form from which the
permanent teeth have been derived. The infundibu-
lum or pit is present, but of comparatively little
depth.
138 THE STKUCTUKE OF THE HOESE.
The canine teeth of the horse evidently belong to
the permanent set, not coming into place until the
animal is full grown, and lasting throughout its
lifetime. It is commonly stated that they have
no deciduous predecessors. On this subject, how-
ever, the following observations of Lecoq are impor-
tant :*
" The canine teeth are not shed, and grow but once.
Some veterinarians, and among them Forthomme and
Rigot, have witnessed instances in which they were
replaced ; but the very rare exceptions cannot make
us look upon these teeth as liable to be renewed.
We must not, however, confound with these except
tional cases the shedding of a small spiculum, or
point, which, in the majority of horses, precedes the
eruption of the real tusks."
These spicules are in all probability the true
milk canines in an extremely vestigial condition ;
their loss, in the gradual process of degeneration of
these teeth, taking place, as might be expected, be-
fore that of their permanent successors. This sub-
ject would well repay a fuller investigation than it has
hitherto met with, as it seems to be another of the
numerous instances of rudimentary structures in the
* Quoted in Fleming's translation of Chauveau and Ar-
loing's Comparative Anatomy of the Domesticated Animals
(1873), p. 352.
THE HEAD AND NECK. 139
horse, pointing to a different condition in the ances-
tral state.
The diminutive first premolars should probably
be regarded as teeth of the permanent set, and, con-
sidering how near they are to disappearance, they
could hardly be expected to have milk predecessors,
especially as such are frequently absent in other ani-
mals in which these teeth are fairly well developed.
The functional milk molars are three in number,
corresponding in succession with the three functional
premolars of the permanent set. The middle one
resembles the intermediate permanent molars, but
the first and third have their extremities somewhat
narrowed, so that the grinding-surface of the whole
block presents a representation on a smaller scale of
that of the permanent set. The crowns are compara-
tively short, and distinct roots are formed by the
time the growth of the tooth is complete. As the
permanent teeth rise up below them these roots are
absorbed, and nothing remains but the worn base
of the crown, which is finally cast off as its successor
becomes fitted to take its place.
Time of Appearance and Order of Succession of the
Teeth. — The eruption or cutting through the gums
of the temporary teeth commences at about the
time of birth, and is complete before the end of the
first year, when the young animal has its full set of
140 THE STRUCTUBE OF THE HORSE.
twenty-four teeth, three incisors and three molars
above and below on each side of each jaw. The
upper teeth, ms a rule, appear somewhat earlier than
those of the Lower jaw. Within a very few days
after birth the central incisors make their appearance,
and by the end of the second week they are fairly
up in the mouth. The first and second molars come
into place about the same time. Between the first
and second month the second (lateral) incisors ap-
pear, then the third molar, and finally (at about
nine months) the third (corner) incisors, which com-
plete the milk dentition. Of the permanent teeth,
the first true molar appears about the end of the first
year, followed by the second molar before the end of
the second year. These teeth are thus in place be-
fore any of the milk-teeth have been shed. At about
two and a half years the first premolar replaces its
predecessor. Between two and a half and three
years the first permanent incisor appears. At three
years the second and third premolars and the third
true molar have appeared, at from three and a half
to foui- years the second incisor, at four to four and
a half years the canine, and finally, at five years,
th<- third (corner) incisor, completing the permanent
dentition. Up to this period the age of the horse is
clearly shown by the condition of its dentition, and
for some years longer indications can be obtained
THE HEAD AND NECK. 141
from the wear of the incisor teeth,* though tliis de-
pends to a certain extent upon the hardness of the
food and other accidental circumstances.
The Lips.
The lips of the horse are remarkably sensitive and
flexible. They can be stretched out in various direc-
tions, and are much u*'<\ in gathering food into the
mouth. Any one who has seen a horse lake a small
piece of sugar from a child's hand will appreciate the
delicacy and efficiency of 1 hese organs as instruments
of prehension. They present a great contrast to the
thick rigid lips of the ox, in which animal the tongue
plays a more important part in the duty of obtaining
food. Flexible and prehensile lips are characteristic
of Hie Perissodactyles. In most species of rhinoceros
the upper lip is prolonged toapoint in the i middle
line, which acts almost like a finger, and in the tapirs
it joins with the nose to form a flexible and very mo-
bile snout or short proboscis.
The Nostrils.
The nostrils of the horse arelarge and very dilat-
able, allowing of the admission of a greater or less
* These are very fully described and illustrated in a
pamphlel called Dentition as indicative of the Age of the Ani-
mals of the Farm, by Professor 0. T. Brown, 2d edit. 1889.
142 THE STRUCTURE OF THE HORSE.
amount of air, according to the demands of respira-
tion. Owing to the great length of the soft palate
and its relation to the upper end of the windpipe,
breathing takes place entirely through the nose.
When men, dogs, and many other animals, in con-
sequence of any great exertion, begin to pant, and
require an additional quantity of air to that wmich
is ordinarily taken in by the nose, the mouth comes
to the aid of that channel, and is widely opened ; but
the horse under the same circumstances can only ex-
pand the margins of the nostrils, for which action
there is a very efficient set of muscles, acting on the
cartilaginous framework which supports them and
determines their peculiar outline. The variations in
the form and amount of dilatation of the nostrils
give great character and expression to this part of
the horse's face.
Immediately within the margin of the upper part
of the nostril is a structure of very considerable in-
terest, which is generally supposed to be peculiar to
the horse and its immediate allies, the use of which
is entirely unknown. It is a blind pouch, three to
four inches in depth, conical in form, though slightly
curved, and lying in the cleft seen in the dried skull
between the nasal and premaxillary bones. It is a
diverticulum from the nasal passage, with which it
freely communicates below, and is lined by a contin-
THE HEAD AND NECK. 143
nation of the same smooth mucous membrane which
lines the passage. In veterinary anatomy it is called
the " false nostril."
If this were all we knew about this organ it would
be unsatisfactory enough, but it immediately acquires
interest when we learn that in the tapir a similar
structure, only in a very much more developed con-
dition, is found. In that animal it runs upwards, as
a long, narrow tube, from the external nostril, at
first in contact with its fellow of the opposite side,
and afterwards, taking a curiously curved course,
terminates in a dilated, closed extremity, which lies
in a distinct groove by the side of the upper part of
the nasal bone. Its walls are cartilaginous, and con-
voluted in such a manner as greatly to increase the
area of the internal surface. It is obvious that the
"false nostril" of the horse cannot be looked upon
as anything specially belonging to the economy of
that animal, but rather as a rudimentary condition
or survival of a structure which is far more highly
developed in some of the more primitive forms of
Perissodactyles. This view is greatly strengthened
by the recent discovery of an exactly similar struct-
ure in the rhinoceros, only in a condition interme-
diate between that in which it is found in the horse
and the tapir *
* E. F. Beddard, Proceedings of the Zoological Society of
Loudon, 1889, p. 10.
144 THE STRUCTURE OF THE HORSE.
Tims, an organ which, when only known in one
animal, appeared strange, anomalous, and puzzling,
because there seemed nothing to account for its
presence, acquires in the light of wider knowledge a
much deeper interest ; for if we cannot yet discover
its purpose, its existence in some modification in all
of these three very distinct forms, and in, as far as
is known, no other mammal, is a strong corrobora-
tion of the view, formed upon other evidence, of their
close affinity and common descent.
In the ass, the pouch is said to be deeper than in
the horse, and areolated at the blind extremity ; but
detailed comparative observations upon its condition
in the different species of existing Equidce and upon
its development in the horse are almost entirely
wanting, and would well repay the trouble the inves-
tigation would cost. The nearest analogue in other
orders of mammals is perhaps the singular pouch
developed from the upper part of the commencement
of the nasal passage of the "bladder-nosed" seal
(Cijstophora cristata), which the animal has the power
of inflating with air when excited. The analogy is,
however, by no means close, as in the seal the pouch
is only found in the male, and not even in the young
of that sex. If the sac in the horse is the remnant
of some organ which formerly played a more im-
portant part in the economy of the race, we should
THE HEAD AND NECK. 145
expect to find it proportionately larger in the younger
individuals of the existing species than in the adults.
Guttural Pouches.
Other equally mysterious structures are the " gut-
tural pouches " — also diverticula of the respiratory
passages — large cavities containing only air, one on
each side, situated at the base of the skull behind
the pharynx, and connected with the Eustachian
tubes (the canals which convey air to the internal
chamber of the ear) and which in the most approved
works on veterinary anatomy are said to be "found
only in solipeds." Exactly similar pouches exist in
the tapir, but I am not aware whether they have as
yet been looked for in the rhinoceros. They have
been supposed to have some use in connection with
the function of hearing ; but it is possible they may
rather be classed with the numerous large air sinuses
found within the bones of the head of the horse, in
common with most other mammals, the object of
which is evidently to give increased volume without
increased weight, and thus to furnish wide surface
for the attachment of muscles and for the support
and protection of various organs situated within the
head.
It has been pointed out that in the artificial con-
ditions under which some domestic horses live, these
146 THE STRUCTURE OF THE HORSE.
pouches may become sources of trouble and even
danger. As they communicate with the nasal cham-
bers by slit-like orifices, when the horse sniffs air is
drawn into them. Should this occur when the ani-
mal is feeding in a manger or nose-bag, or the food
is dusty, minute particles may enter the pouches and
set up inflammation, or give rise to the formation of
solid concretions. There is reason to believe that
millers' horses are more liable to these affections than
others.*
The Neck.
The skeleton of the horse's neck is formed of seven
vertebra?, the same number as in man, and with very
few exceptions, indeed, in all other mammals, whether
the neck itself be short or long.
The skull is attached to the first vertebra of the
neck, called the atlas, by a deep "ball-and-socket"
joint, which allows of motion in various directions.
The two projecting condyles of the skull together
form the ball, which fits into the hollow front surface
of the atlas. This vertebra also turns freely on the
second, or the axis, and there is a certain but more
limited amount of motion at each of the succeeding
five joints. The combined action of these numerous
joints permits of very free play to the head in all re-
quired directions.
* See J. Bland Sutton, Evolution and Disease (1890), p. 94.
THE HEAD AND NECK. 147
The neck joins the front end of the thorax or
chest, the skeleton of which is formed by the dorsal or
thoracic vertebras above, the sternum or breast-bone
below, connected together by the hoop-like ribs. As
seen in the figure (Frontispiece), the cervical or neck
vertebras are flat above, but those of the thoracic
region have long processes projecting upwards, and
forming together the ridge of the middle of the back.
Those of the third, fourth, and fifth vertebra?, which
are situated between the shoulder-blades, are the
longest, and correspond externally to the " withers,"
the highest point of a horse's back, across wliich the
measuring-rod is placed when taking his height.
The upper contour of the neck of the living horse
is altogether different from that of the skeleton, the
great depression seen in the latter in front of the
high spines of the thoracic vertebras being filled up
in the middle line by a remarkable structure called
the " cervical ligament," and on each side of this by
large masses of muscles which raise and turn the
head, and above all by the median " crest," a soft,
but firm, fibrous, and fatty ridge immediately beneath
the skin from which the mane grows.
The cervical ligament (ligamentum cervicis, liga-
mentum nuchce or "pack wax") which in man is
quite rudimentary, as his head, balanced on the top
of the vertebral column, requires no special support,
148 THE STRUCT UEE OF THE HOESE.
is immensely developed in the horse. It consists
mainly of a strong elastic cord, which is attached in
front to the upper part of the back of the skull (Fig.
22, O), and posteriorly to the elongated spines of the
dorsal vertebrae (S). Between this, the funicular
part of the cervical ligament, as it is called, and the
bones of the neck, fibers of the same material, pass
downwards and forwards, to be attached to the up-
per surface of all the different cervical vertebra?, ex-
cept the atlas, forming a lamellar part, which lies in
the middle line dividing the muscles of each side of
the neck. This structure, though called a ligament
for want of a better name, differs from the true liga-
ments, which connect bones together at the joints, in
being of a yellow color and in having in a very marked
degree the property of elasticity. It will bear con-
siderable stretching, and then will return again to
its normal length, which a true ligament composed
of ordinary white fibrous tissue will not do.
Elastic material is often made use of in the animal
economy to great advantage mechanically, restoring
without effort to its proper position a part which
has been temporarily disturbed from it, and thereby
saving a vast expenditure of muscular power. The
valves of an oyster or a cockle-shell are opened by
an elastic hinge and closed by contraction of a mus-
cle placed between them. Under the ordinary con-
THE HEAD AND NECK.
149
ditions of life it is necessary that they should remain
open in order that the water containing air and nutri-
ment may pass freely over the gills and month of
o
Fig. 22. — The cervical ligament, and bones to which
it is attached (from Leisering). 0, occipital crest
of skull ; 1 to 7, the seven cervical vertebrae ; S,
spinous processes of the anterior dorsal vertebrae.
the animal. They only need to be closed occasionally
on the approach of some dangerous enemy. To
close the valves and to maintain them in this position
requires an effort ; directly this effort is relaxed they
150 THE STEUCTUEE OF THE HOESE.
open again by the simple mechanical effect of the
elastic ligament. If they had to be opened and
maintained in the open position, by a muscular effort,
a far greater expenditure of power would be required
on the part of the animal. In the same way in our
own breathing, in which the air is alternately drawn
in and expelled from the lungs by the expansion
and contraction of the chest-walls, nearly half the
labor, with corresponding expenditure of energy and
waste of muscular tissue, is saved by the application
of elasticity as the principal cause of the contraction
which follows each muscular effort by which the act
of expansion is performed.
As already mentioned, the horse's head, owing
chiefly to the immense apparatus required to grind
its necessary supply of food, is of great weight, and
if it had to be supported at the end of the long neck
entirely by a muscular effort on the part of the ani-
mal, great expenditure of force, requiring a still
larger supply of food to keep it up, would take place.
But, thanks to the structure, attachments and phys-
ical properties of the cervical ligament, it is no effort
whatever to the horse to keep its head in the proper
position. In fact, this ligament is so disposed, and
of such strength and elasticity, as to allow the head
to be moved up or down or from side to side, as re-
quired, by a very slight exertion of muscular action,
THE HEAD AND NECK. 151
but directly this ceases to return it to the position
best suited for a state of repose.
Probably, if those who have to do with the har-
nessing of horses were better acquainted with this
admirable mechanical apparatus for holding up the
head in a natural and unstrained position, they would
think it less necessary to supplement the cervical
ligament by an external contrivance for effecting
the same object, called the " bearing-rein," which,
however, not being elastic, never allows the head,
even momentarily, to be altered in position • which
is generally fixed so tightly as to interfere greatly
with the natural graceful curve of the neck, one of
the horse's chief beauties ; and which, being attached
at one end through the tender corners of the mouth,
must, if short enough to effect the object for which
it is used, be a continual source of pain or irritation
to the animal.
Of the numerous petty cruelties practiced by man
upon the domestic animals in obedience to the dic-
tates of fashion or custom, or out of mere thought-
lessness, the use of the bearing-rein as a regular part
of the harness of a carriage or cart-horse is one of
the least excusable. We may, notwithstanding all
the protests of the sensible, continue, from the same
motives, to deform and injure our own feet by pointed
shoes, and our own waists by tight lacing, but we
11
152 THE STRUCTUKE OF THE HORSE.
ought to extend more consideration to the comfort
and welfare of the helpless animals, which, for our
own advantage, we have taken under our care *
* See Bits and Bearing-reins, with observations on Horses
and Harness, "by E. F. Flower, London, 7th edit. 1885.
CHAPTER IV.
THE STRUCTURE OF THE HORSE — (continued).
TEE LIMBS.
General characters of the limbs of vertebrated animals — Com-
parison of the skeleton of the fore limb of the horse with
that of man — Comparison of the skeleton of the hind limb
of the horse with that of man — The muscles of the limbs
— The warts or callosities on the external surface of the
limbs — The ergot or spur — The chestnuts, or mallenders
and sallenders — The hoofs.
General Characters of the Lbibs of Verte-
brated Animals.
The body of all vertebrated animals consists of
a main or axial portion, the "trunk/' terminating
anteriorly in the head, and posteriorly usually more
or less prolonged into a tail. The skeleton of this
part consists of the skull, the vertebral column, and
the ribs and sternum or breast-bone. All the organs
essential to life are contained in the axial part of the
body, and in some animals, as serpents and a few
fishes, it is the only part present. In the very large
majority of animals, however, there are added append-
154 THE STRUCTURE OF THE HORSE.
ages, called " limbs," mainly adapted for the purposes
of locomotion, and which are attached to the trunk
by the intervention of solid structures, commonly
called in anatomical language " girdles." These are
so called because the pair of them, when completely
developed, nearly encircle the body ; but it must be
admitted that it is not a very happy expression, as,
except through the intervention of the vertebral col-
umn, they never form complete circles, and very
often the " semigirdles " of each side are widely sep-
arated both above and below *
These girdles and the limbs which they support
are never more than two in number on each side, and
are almost always placed, the one near the front,
and the other near the hinder end of the trunk.f
The anterior girdle and limb are often called " pec-
toral," and the posterior " pelvic," from the regions
of the body in which they are situated. Though in
the large majority of vertebrated animals both pairs
of limbs are present, either one or the other may
be in a very rudimentary condition, or even alto-
* The semigirdles are sometimes called "arches," which
is hardly more expressive, as, though the word means a seg-
ment of a circle in any position, the transverse position is
now almost universally associated with it.
t In some fishes the ventral fin, which corresponds to the
hind limb of most vertebrates, is placed below, or even an-
terior to the pectoral fin, or true front limb.
THE LIMBS. 155
gether wanting, though in such cases some trace of
a girdle is nearly always found.
The limbs belonging to the same region of the
different sides of the body resemble each other in all
essential particulars, being symmetrical paired or-
gans. The anterior and posterior limbs have a gen-
eral resemblance in plan, although always differing
in certain details, these differences becoming more
marked when the limbs have different functions to
perform. Thus, as in birds, the fore limbs may be
modified into wings for flight, while the hind limbs
are only used for walking on the ground ; in which
case the fundamental resemblance of the two is very
much masked. In the horse, as we shall see, where
they are all used for the same purpose, standing,
walking, or running on the ground, the fore and hind
limbs are remarkably similar in construction, per-
haps as much or more so than in any other animal.
The fore and hind limbs resemble each other
mainly in being divided primarily into three seg-
ments : one proximal, or nearest the body and ar-
ticulated with the girdle which carries it ; one middle
segment, and one distal or farthest from the body.
The proximal segment has in both cases a single
bone forming its supporting axis, which bone is called
the humerus or arm-bone, in the fore limb, and the
femur or thigh-bone in the hind limb. The middle
156 THE STEUCTUEE OF THE HOESE.
segment of both limbs has two bones lying side by
side — the radius and ulna in the fore limb and the
tibia and fibula in the hind limb. The joint by which
the proximal segment is attached to the correspond-
ing girdle is called " shoulder" in the fore limb, and
" hip " in the hind limb ; that between the first and
second segments is called the "elbow" in the fore
limb and the " knee " (the " stifle " in the horse) in
the hind limb (see the skeleton of the horse and man
in Frontispiece).
The distal or third segment is of more complex
character. It constitutes in the fore and hind limbs
respectively the " hand " and " foot " of man, the fore
and hind "foot" of quadrupeds, or, in more precise
anatomical language, of general application to all
animals, the manus and the pes. Each of these con-
sists of a group of small bones at its proximal end,
forming the carpus or wrist in the fore limb and the
tarsus or ankle in the hind limb. Beyond these it
always has a tendency to divide up into a number of
rays, called digits, fingers, or toes (see Fig. 1, p. 15).
Leaving out of consideration certain vestigial
structures which are held by some anatomists to in-
dicate the possibility of the former existence of a
larger number of digits, no known mammal has more
than five digits in each limb. For the convenience
of description the digits are distinguished by the
THE LIMBS. 157
numerals I. to V., counted from the radial to the ulnar
side in the fore limb, from the tibial to the fibular
on the hind limb. They are also sometimes named
— (I.) pollex or thumb (fore limb), hallux (hind limb) ;
(II.) index; (III.) medius ; (IV.) annularis;* and
(V.) minimus. Though five is the complete number,
one or more may be in a very rudimentary condition,
or altogether suppressed. If one is absent, it is most
commonly the first ; next follows the fifth. The
third is never lost, although either the second or
fourth, or both, may be absent.
In both limbs the normal arrangement is that
the carpus or the tarsus, as the case may be, supports
five long bones placed side by side, called the meta-
podials (or metacarpals in the fore limb, metatarsals
in the hind limb), and to the end of each of these are
three distinct bones called phalanges, except in the
case of the pollex and hallux, which have only two.
The terminal or distal phalanges of the digits are
often specially modified to support the external horny
covering usually present, called nail, claw, and hoof,
according to its form and size, and hence are spoken
of as the " ungual phalanges." -
This portion of the limb, being usually more or
less broadened and flattened, presents two surfaces
* Being in man the finger on which the ring is commonly
worn.
158 THE STRUCTURE OF THE HOESE.
and two edges and borders. The surfaces are dor-
sal, which in the ordinary position of the feet of most
mammals is turned forwards or upwards (the " back "
of the human hand), and ventral, or palmar in the
fore limb or plantar in the hind limb, turned back-
wards or downwards. The edges are external (ulnar
in the fore and fibular in the hind limb) and internal
(radial in the fore and tibial in the hind limb).
The flexure between the middle and distal seg-
ments of the limb is called the " wrist- joint " and
" ankle-joint " in the fore and hind limbs respectively
in man, which correspond with those called the
"knee" and the "hock" in the horse.
These are the essential characters in which the
fore and hind limbs resemble each other. Of the
differences many are merely adaptive to the different
purposes to which they are put. The perfect effi-
ciency of action, even in those that bear the closest
resemblance, is secured by a partial rotation on its
axis of each from the shoulder or hip, as the case may
be, so that the outer side of the hind limb at the uext
joint comes to correspond with the inner side of the
fore limb ; but, owing to a second rotation in the
middle segment in the latter, the last segments, or
hand and foot, are brought again into corresponding
positions in the ordinary walking attitude, the first
(radial and tibial) digits being on the inside edge, and
THE LIMBS. 159
the fifth (ulnar and fibular) on the outside. Besides
these differences, there are others, the signification of
which is not so clear, constantly met with in the ar-
rangement of the bones of the carpus and tarsus.
Moreover, it may be noted that the joint between the
first and second segments of the hind limb (knee-
joint) has almost always a special bone {patella or
knee-cap), which is wanting in the fore limb.*
Tins general description will include such different
limbs as those of a man, a seal, a bat, and a horse, all
formed on the same common plan, but all modified
for the different purposes they have to fulfill. We
must now treat in greater detail the peculiarities
of the limbs of the horse, and to render them more
intelligible another form is required for comparison.
We will therefore take that with which we are all
most familiar, and commence with a comparative
account of the bones of the fore limb in man and in
the horse.
Comparison of the Skeleton of the Fore Lbib
of the Horse with that of Man.
To begin with the shoulder-girdle. In the full-
grown man this consists of two bones, the scapula
* For further description of the correspondences and dif-
ferences of the bones of the fore and hind limbs, see the au-
thor's Osteology of the Mammalia, p. 361, 3d ed., 1885.
160 THE STRUCTURE OF THE HORSE.
or "true shoulder-bone/' or "blade-bone" (which is
itself composed in infancy, and in some animals per-
manently, of two separate bones, the scapula proper
and the coracoid), and the clavicle or " collar-bone/'
a strong curved bar, united at its outer end with the
scapula, and at its inner end with the sternum or
breast-bone. The scapula is of complex shape, with
strong projecting processes. In the horse (see Fron-
tispiece) the humerus especially, so prominent a fea-
ture in the scapula of man, being scarcely visible.*
There is no trace of a clavicle. The scapula and the
limb attached to it are not in any way joined to the
rest of the skeleton by bone, but only by the muscles
which pass from one to the other. The trunk is, in
fact, only slung between the two shoulder-bones.
These differences are entirely related to the differ-
ent use and motions of the fore limb in man and the
horse respectively. In man the humerus moves at
the shoulder- joint in every direction. It can be
swung round so that its outer end forms a complete
circle. The muscles by which these actions are per-
* Wineza has recently shown that in the early embryonic
condition of the scapula of the horse this process is relatively
much larger than in the adult. This is in conformity with
the general law that the young show the more generalized,
and the old the more specialized condition. He was unable
to detect any sign of a clavicle. Morphdhg. Jahrb. Bd. xvi.
(1890), p. 647.
THE LIMBS. 1G1
formed require for their attachment outstanding
ridges on the scapula. This bone, moreover, requires
to have a certain degree of fixity, especially provision
against its being driven too far inwards or outwards
during the lateral action of the arms. This is pro-
vided for by its being connected to the sternum by
the intervention of the clavicle. In the horse there
is practically but one action at the shoulder, and
that not a very extensive one — a fore-and-aft hinge
scapula is a very much simpler bone, long, narrow,
flat, with the processes much less developed, the
acromion motion. The fore limbs are never crossed
forwards across the chest, or thrown upwards behind
the back, as with our arms, and hence there is no
necessity for a clavicle, and the muscles which pass
from the scapula to the humerus, though present, are
developed in a very different degree.
Corresponding with the freedom and play of
movement of the human arm and hand, the first bone
of the limb proper, the humerus, in man is long and
slender and has a large globular upper extremity or
" head," which plays freely in the shallow, cup-like
(glenoid), articular surface of the scapula, constitut-
ing a true ball-and-socket joint. In the horse, on the
other hand, the humerus is comparatively short and
stout,* and its movements are extremely limited. It
* The actual length of the humerus of an average-sized
horse and man is almost identical, as seen in Frontispiece.
1G2 THE STRUCTURE OF THE HORSE.
is, in fact, so short, and placed so nearly horizontally,
and so covered np with muscles, that externally this
segment makes no distinct appearance, being bnried in
the body or trunk, from which the limb only separates
itself at the commencement of the second segment
or elbow-joint, instead of at the shoulder, as in man.
The skeleton of the second segment or forearm in
man consists of two bones placed side by side — (1)
the ulna, which is connected with the humerus by a
simple hinge-joint, allowing motion of bending (flex-
ion) and straightening (extension) only in oue plane,
and (2) the radius, which turns or rotates in a pecul-
iar way round the former, carrying the hand with it,
and thus enabling the palm or the back of the hand
to be turned uppermost at will — motions described as
"supination" and "pronation." In the horse there
is nothing of the kind ; the radius is a strong bone
of almost equal size at both ends, and the ulna is
reduced to its upper part, which is firmly fixed to the
radius, its only function being to strengthen the very
perfect hinge of the elbow-joint behind. The hand
is thus permanently fixed in the prone position, with
its dorsal surface turned forwards. A flexible and
revolving wrist- joint, though essential to the perform-
ance of the duties required from the human hand,
would be quite incompatible with those needed from
the corresponding part of the horse.
THE LIMBS. 163
The consolidation of parts into a single support-
ing column, so conspicuous in the forearm, is carried
out to a still greater extent in the last segment of the
limb of the horse. The eight carpal bones of the hu-
man hand are, it is true (with one exception, the tra-
pezium, the inner bone of the distal or lower row,
which supports the thumb), all present, even to the
pisiform, which projects backwards from the others
on the outer side of the wrist. These bones are,
however, more solidly compacted together than in
the human hand, the flat surfaces by which they come
in contact scarcely allowing a trace of movement be-
tween them. The metacarpus consists mainly of one
great bone, the " cannon-bone " of veterinarians, rep-
resenting the third or middle metacarpal of the hu-
man hand (3m, Fig. 6, p. 39). Lying on each side
of this, and generally in full-grown animals united
with it, are two smaller bones, the "splint-bones" of
veterinary anatomy (2m and 4m). These represent
respectively the second and fourth metacarpals of the
human hand. Above they have thickened heads,
which articulate in the usual manner with the carpal
bones ; but below they taper off .almost to nothing,
ending some way above the lower end of the great
middle bone. The part commonly called the " lyiee "
of the horse thus corresponds to the back of the wrist
of man, and everything beyond or below it corre-
164 THE STKUCTUKE OF THE HOESE.
sponds to the hand proper, the hinder surface being
the palm, long and narrow in the horse, as it is short
and broad in man. As only one metacarpal bone is
fully developed, there is bnt one digit or finger, which,
as in man, has three bones (phalanges, p\ p\ and p\
Fig. 6), connected by hinge-joints, allowing only the
motions of bending or straightening backwards and
forwards. The first phalanx is somewhat elongated,
the next very short, and the last (the nngnal phalanx)
very broad and of a peculiar semilunar form. These
bones are in veterinary anatomy called respectively
the " large pastern " or os suffraginis, the " small pas-
tern" or os corona, and the " coffin-bone" or os pedis.
The joint between the metacarpal and the first pha-
lanx is the " fetlock," that between the first and sec-
ond phalanges the " pastern," and that between the
second and third phalanges the " coffin- joint."
There are several other small bones in the horse's
foot which must be mentioned, and which belong to
the group called " sesamoids," bones developed in ten-
dons where they play over joints. In the human
hand there is a pair of these over the palmar surface
of the metacarpophalangeal joint of the thumb, but
none are developed in the other digits. In the horse
there are three, all also on the palmar surface (or be-
hind in the natural position) ; a pair of nodular form
placed side by side over the metacarpophalangeal
THE LIMBS. 165
articulation (Fig. 6, *), and a single large, transversely
extended one (Fig. 6, s-1), called the " navicular" bone,
behind the joint formed between the second and third
phalanges.
In standing at rest in the natural position the
forearm and the metacarpus are nearly upright, and
the three bones of the digit or finger form a nearly
straight line with them, but inclining forwards at
the lower end. The third, or ungual phalanx, alone
rests, through the intermedium of the hoof, upon the
ground, and receives the whole of the weight of one
quarter of the animals body.
The main peculiarities of the skeleton of the fore
limb of the horse are these : the absence of clavicle,
the elongated, narrow and flat scapula, the short and
obliquely placed humerus, the consolidated radius
and ulna, the immensely developed middle metacar-
pal and its digit, and the suppression of all the
others. Moreover, all the joints from the shoulder
downwards are simply hinge- joints, allowing free
fore-and-aft flexion and extension, but scarcely any
movement in any other direction.
Comparison of the Skeleton of the Hind Limb
of the Horse with that of Man.
The pelvic differs essentially from the pectoral
girdle, inasmuch as it is firmly fixed to the trunk, to
166 THE STRUCTURE OF THE HORSE.
fit it for the more important part the hind limb takes
in sustaining and propelling the body in walking
and running. Several of the vertebras of this region
are united into a solid block, the sacrum, to the sides
of which the upper part of each arch or semigirdle
is in the closest contact by a large flat surface, and
firmly bound by strong ligaments. The arches are,
moreover, united to each other in the middle line be-
low, without the intervention of anything corre-
sponding to a sternum or clavicle. On the outer
side of each semigirdle is a deep round cup-shaped
depression, the acetabulum, into which the head of
the first bone of the limb proper is received, and
which therefore corresponds with the glenoid fossa
of the shoulder. The joint at this position is the
" hip- joint." There is no essential anatomical dif-
ference in the construction of the "pelvis," as the
whole girdle is called, in man and in the horse, each
lateral half being in both originally composed of
three distinct bones — the ilium, the ischium, and the
pubis — which unite before the animal is full grown
to form a solid mass, which has received from the
old anatomists the curious name of os innominatum.
The actual form of the bones presents consider-
able differences, the comparatively broad and basin-
like pelvis of man relating chiefly to the adaptation
of the body to the upright position.
THE LIMBS. 167
The bone of the first segment of the limb proper
is called the femur or thigh-bone. As in the corre-
sponding bone of the fore limb, it is in the horse
comparatively stout and short, and placed very ob-
liquely, the lower end advancing by the side of the
body, and being so little detached from it that the
knee-joint appears to belong as much to the trunk
as to the limb j a position altogether in contrast to
that of the knee of man, separated from the body
by the whole length of the elongated, free, vertically
placed thigh (see Frontispiece). The bone itself has,
in addition to the usual two rough processes near
the upper end for the attachment of muscles (the
trochanters) found in man and other mammals, a
prominent compressed ridge, curving forwards,
placed on the outer edge of the shaft of the bone,
somewhat lower down than the other two. This,
the so-called " third trochanter," as mentioned in the
first chapter, is characteristic of all known Peris-
sodactyles, and is also found in some rodents, but
not in man or in mammals generally.
The second segment of the skeleton of the hind
limb is represented in the horse almost entirely by
the tibia. The fibula, indeed, is present, and a dis-
tinct bone, but only appears as a slender styliform
rudiment of the upper portion attached to the outer
side of the tibia.
12
168 THE STKUCTUKE OF THE HORSE.
The third segment of the hind limb, the foot or
pes j has undergone precisely similar changes from
the generalized or typical form to those already
described in the fore limb. In fact, below the car-
pal and tarsal bones (the "knee" and "hock" of
the horse respectively) the fore and hind limbs are
almost exact repetitions of one another. The great
development of the third metatarsal bone, the rudi-
mentary condition of the second and fourth, the
complete absence of the first and fifth ; the presence
of only one digit, consisting of three phalanges, hav-
ing almost precisely the same form (except that
they are rather narrower in the hind than the fore
foot), are common to both extremities. In this
structure of the foot, especially in the possession of
but a single toe on each limb, the horse is absolutely
unique among mammals. A very small Australian
marsupial (Chmropus castanotis) has but one func-
tional toe (in this case the fourth), on the tip of
which it walks, on the hind foot, but three other
toes are present, and complete in all their parts,
though very minute ; and in the fore foot two
nearly equally developed toes reach the ground.
As the first segment of the horse's hind limb is
so much shorter proportionately than that of man,
the last is as much longer, and being habitually car-
ried in a totally different position has a very differ-
THE LIMBS. 169
ent appearance. The backwardly projecting promi-
nence in the hock of the horse corresponds to the
heel of man, and the hinder surface of the horse's
limb, from the hock to the hoof, corresponds to the
plantar surf ace or " sole " of the foot of man. Man
is " plantigrade," the whole of the sole of the foot,
including the heel, being placed on the ground in
standing ; the horse is " unguligrade," walking only
on the hoof, incasing the tip (or last phalanx) of the
toe. Dogs and cats assume an intermediate position
(" digitigrade w), for, although the metatarsal bones
and the heel are raised, not only the tips, but the
greater part of the plantar surface of the toes rests
on the ground.
The sesamoid bones of the hind foot exactly re-
semble those of the fore foot.
The Muscles of the Limbs.
Muscles are the organs by which all the move-
ments of one part of the body in relation to any
other part are effected. They lie around the bones
and beneath the skin, giving the external form to the
animal, and constituting what is commonly called its
flesh.
Muscular tissue is composed of a great number
of exceedingly minute parallel fibers of peculiar
structure, and it differs from all other tissue in pos-
170 THE STRUCTURE OF THE HORSE.
sessing the property of contracting in length (with
corresponding dilatation in width) on the application
of a stimulus, usually conveyed to it through the
nerve the terminal fibers of which are distributed
through it. The electric current, or mechanical irri-
tation, will act as a stimulus to contraction, but in
the living state the will of the animal, conveyed from
the brain along the nerve to the muscle, is the usual
cause of action. If the nerve is divided anywhere in
its course between the brain and the muscle, the lat-
ter will no longer act in obedience to the will, and is
said to be paralyzed, although it does not really lose
its power of contraction, as may be proved by the
application of any other appropriate stimulus either
directly to the muscle or to the lower part of the di-
vided nerve.
In order that muscles by their contraction may
produce movements, they must be fixed by their two
extremities to two different bones, which are con-
nected to each other by a movable joint. When the
contraction brings the ends of the muscle nearer to-
gether than they were before the bones must follow,
and their position in relation to one another must be
changed. It usually happens that one attachment
of a muscle is to a point more fixed than the other,
and this is then spoken of as its " origin " ; the at-
tachment to the bone that is most movable being
THE LIMBS. 171
called the " insertion." This distinction is, however,
not always a satisfactory one, as most muscles may
act on occasions either way. In the limbs, where the
muscles lie more or less parallel to the long bones, it
is convenient to speak of them as arising at the end
nearest the body, and being inserted at that farthest
from it. As a general rule this accords with their
action.
The muscles are sometimes attached directly to
the bone, or rather to the fibrous sheath (periosteum)
which closely invests it, but very often, for obvious
mechanical reasons, they are connected with the
bones by the intervention of " tendons," strong non-
elastic fibrous cords, which are fixed to the muscle at
one end and the bone at the other. It is in the limbs
especially that tendons play a prominent part, as it
is far more convenient that many of the strong mus-
cles that move the fingers and toes should not be
placed close to the parts on which they act, as if they
were they would give a very clumsy form to the limb.
They are, therefore, situated higher up, near the body,
where increased thickness and weight of the limb are
no disadvantage, and they produce their effect on
the toes through the intervention of long tendons,
which run close down the side of the bone.
As all the joints of the limbs of the horse are sim-
ply hinge-joints, acting only in one plane, the muscles
172 THE STRUCTURE OF THE HOESE.
are almost all either simple " flexors/' bending the
distal segments backwards on the segment above, or
" extensors/7 returning them to the straight position.
The structure of the joints prevents the segments be-
ing bent forwards much beyond a straight line with
the segment above. The extensors are placed upon
the anterior or dorsal, and the flexors on the pos-
terior or ventral surface of the limb.
In the human arm and hand there are muscles
having many other functions, such as turning the
hand round, spreading the fingers and bringing them
in contact again, which, of course, are not required
in the horse. In the limbs of all mammals having
the typical number of five digits completely de-
veloped, the muscles, as might be supposed, are as
numerous and arranged on much the same general
plan as in man. It is, however, very remarkable
that in the horse's limbs many more muscles exist
than would be thought necessary for the very simple
actions they have to perform. But it appears that
the reduction of bones to a rudimentary condition,
as in the case of the ulna and the fibula, or their en-
tire loss, as in the case of four of the toes, has taken
place more thoroughly than, and in advance of, that
of the muscles which were originally connected with
these bones, many of which linger, as it were, behind,
though with new relations and uses, sometimes in
THE LIMBS. 173
a most reduced and almost, if not quite, function-
less condition, and sometimes even with completely
changed structure.
From this point of view the muscles of the horse's
limbs form a most interesting study. It has been
truly said by Dr. G. E. Dobson,* that if no other
evidence were obtainable of his five-toed ancestors,
the condition of the muscles of the foot would suffi-
ciently indicate them.
In the fore limb, where the ulna is represented
only by the olecranon (projection of the elbow) and
a greatly attenuated upper part of the shaft, and the
digits reduced to one, most of the forearm muscles
of the five-toed mammals are represented, the proper
extensor of the fifth digit (extensor minimi digiti) even
surviving, although both its insertion and special
function have been completely altered. In the hind
limb the two flexors of the toes (flexor digitorum lon-
gus and flexor hallucis longiis) are both present, with
well-developed tendons united in the foot as in the
great number of five-toed mammals.
It must not, however, be supposed from what has
just been said that anything like all of the numerous
muscles that are developed in the hand of man, with
its versatile functions, can be traced in the horse.
* " On the Comparative Variability of Bones and Muscles,"
etc. Journal of Anatomy and Physiology, vol. xix. p. 16.
174 THE STRUCTURE OF THE HORSE.
That would be obviously impossible with such a re-
duction of the bony elements. The difference (far
less marked in the upper part of the arm) is espe-
cially pronounced in the last segment or manus, or
hand proper, where the fifteen intrinsic muscles of
the human hand are represented by only five * in the
horse. Four of these — the two inter ossei and the two
lumbricales — are in a very greatly reduced condition ;
and the fifth, the short flexor (represented in the hu-
man foot by the muscle called the " first plantar in-
terosseous n)j is a remarkable instance of a structure
not becoming rudimentary and useless, but, while re-
taining its size, position, and connections, being di-
verted from its original purpose and completely
changing not only its function, but its structure. It
is termed in veterinary anatomy "the suspensory
ligament of the fetlock," and appears as a very strong
band or cord of non-elastic fibrous tissue, lying close
to the back of the large metapodial bone, attached
above to the posterior surface of the upper extremity
of this bone, and at its lower end dividing into two
portions, which, diverging from each other, embrace
the metatarso-phalangeal or fetlock joint, and are
inserted partly into the sesamoid bones and partly
into the extensor tendon on the dorsal aspect of the
* This is the number according to the usual statements,
but recent careful dissections have shown traces of others.
THE LIMBS. 175
first phalanx (see Fig. 25, 10, p. 191). The obvious
mechanical use of this ligament (as it has now be-
come) is to prevent over-extension of the fetlock-joint.
If it is ruptured or stretched the animal becomes
what is termed in veterinary language "broken
down'7 — i.e., the fetlock-joint sinks down, and the
hoof has a tendency to tilt forwards and upwards.
" The most interesting point, however, in con-
nection with this structure is that it bears its history
on its face. Almost invariably two thin streaks of
striated muscular fiber are to be found on its super-
ficial surface, leading down to its two inferior divis-
ions. Again, on examining its deep surface, two
very distinct strands of pink fleshy tissue are always
observed extending throughout the entire length of
the ligament. These consist in each case of short,
oblique, striated fibers converging towards the mid-
dle line of the ligament. They represent those mus-
cular fibers of the two heads of the flexor orevis
which have not yet been converted into fibrous tis-
sue. On making a thin microscopic transverse sec-
tion the muscular fibers are seen to sink deeply into
its substance, but it is altogether so small in amount
in comparison with the bulk of the ligament that it
can exercise no function whatever." *
* D. J. Cunningham, Zoology of the Voyage of H. M. S.
Challenger, Part XVI. Keport on the Marsupialia, p. 95.
176 THE STEUCTUEE OF THE HOESE.
The Warts or Callosities on the External
Surface of the Limbs.
The external covering, integument, or skin of the
horse is generally smooth, thick, and tough • much
thicker on the back, flanks, and exposed portions of
the limbs, and thinner on the under and more pro-
tected parts. Like the same structure in all other
mammals, it is composed of two very distinct parts :
(1) An inner, thicker layer, made up of interlacing
filaments of tough, fibrous tissue to which blood-
vessels and nerves are abundantly distributed, and
which also contain muscular fibers, and, in its deeper
portions, small collections of fatty tissue, and every-
where numerous minute glands of two kinds, sudor-
iferous and sebaceous, the former secreting a watery
fluid (the perspiration or sweat), and the latter an
oily substance which lubricates the skin and hair.
This layer is called the derm or coriiim. (2) Lying
upon this, and formed as an exudation or secretion
of its outer surface, is a layer called the epidermis,
not sensitive, and without blood-vessels, soft and
moist in its deeper, and therefore newly-formed
strata, and hard and dry at its exposed surface. It
is not fibrous, but composed of cells which are at
first nearly spherical or polygonal, but gradually be-
come flatter and more scale-like as they approach the
THE LIMBS. 177
surface. Over the greater part of the skin it forms
an exceedingly thin layer, which, nevertheless, serves
as a protection to the softer and more sensitive derm
below ; but in certain parts it accumulates in solid
masses of various forms, constituting the hairs,
horns, nails, claws, hoofs, etc. Wherever these great
accumulations take place, the superficial part of the
derm is specially modified so as to afford a larger
vascular surface available for their production, being
covered sometimes with ridges or lamellce, but more
often with more or less elongated conical or cylin-
drical projections called papittce. Each hair grows
on such a papilla, which is sunk in the bottom of a
follicle or deep pit in the derm or true skin. Under
whatever form it appears, the epidermis is continu-
ally being removed at the surface, flaking or peeling
off in minute fragments, or being worn and ground
away by the contact of external substances, or, as in
the case of hairs, cast off entire. The loss is, how-
ever, compensated by the continual renewal of the
tissue from the surface of the derm below.
The greater part of the limbs of the horse is cov-
ered by an even coat of short hairs, but on the
hinder part of the last segment these are much elon-
gated, and especially at the prominence behind the
joint between the metapodial bone and the first pha-
lanx of the digit, where they form a considerable
178 THE STRUCTURE OF THE HOESE.
tuft or lock, which has given the name of ''fetlock"
(i.e., foot or feet lock) to this part of the horse's limb.
The amount and coarseness of this growth of hair
varies much with the breed of the animal. The
prominence itself is formed partly by the sesamoid
bones, but also, in the middle hue, by a mass of
dense adipose tissue (the "fatty cushion of the fet-
lock"). On the center or most prominent part of
this can be seen, on both fore and hind limbs, when
the hail' around it is clipped off, a roundish, bare
patch (Fig. 23, C, b, p. 179 j Fig. 25, 19, p. 191), cov-
ered with a rough, thickened epidermis, called in
French veterinary works the ergot, as sometimes the
epidermis accumulates on it to such an extent as to
produce an appearance comparable to a spur.
The area of this bare patch is relatively larger in
the ass than in the horse.
I am not aware that the significance of this pe-
cidiarly modified and hairless spot of skin, with its
fatty cushion beneath, has ever been pointed out ;
nevertheless, although generally not noticed at all,
or dismissed in a few words, in all works on horse
anatomy, it is, when properly understood, one of the
most interesting features of the external and visible
structures of the animal's body.
If we look at the palm of our own hand (which,
as shown before, corresponds with the hinder sur-
A.
B.
^ - ;,m}i -lis.
^^W
a.
c.
-
ill
>'•«' ^
tvi ,«<
mm
m.
Fig. 23.— Plantar surface of the foot of— A, man ; B,
dog; C, horse. The letters a, b, and c indicate
the corresponding points of the three. Compare
also Fig. 7, p. 47.
180 THE STEUCTUEE OF THE HOESE.
face of the fore limb of the horse below the so-called
"knee"), we see slight prominences just behind the
root of each finger and opposite the knuckles on the
back of the hand, which mark the position of the
joint between the metacarpal bones and the first
phalanges of the digits. Over these, especially when
the palm is subject to pressure and friction from
hard manual labor, the epidermis is somewhat thick-
ened. The sole of the foot presents exactly the same
arrangement. In such an animal as a dog or a cat,
in which this part of the foot comes to the ground in
walking, there is a large trilobed prominent, bare
pad (Fig. 23, B, 6), composed of a thick fatty cushion,
covered with a hardened epidermis, generally of a
black color. There are also smaller pads in front of
this on the under surface of each of the toes, but the
large one corresponds with the coalesced three middle
prominences of the human palm or sole just noticed.
In the horse's nearest living relatives, the tapir
and rhinoceros, the same arrangement holds good.
There is a large pad under the forepart of the middle
of the foot, which in these animals rests on the
ground, and also a hard sole under each toe (see Fig.
7, p. 47). Now the ergot of the horse clearly, both
by structure and position, corresponds to the palmar
or plantar pads of those animals which walk more or
less on the palm and sole. Owing to the modified
THE LIMBS. 181
position of the horse's f oot, standing only on the end
of the last joint of the one toe, this part of the foot
no longer comes to the ground, and yet the pad with
its bare and thickened epidermic covering, greatly
shrunken in dimensions and concealed among the
long hair around, and now apparently useless in the
economy of the animal, remains as an eloquent testi-
mony to the unity of the horse's structure with that
of other mammals, and its probable descent from a
more generalized form, for the well-being of whose
life this structure was necessary.
The ergot of the horse, placed in the middle hue
of the foot, must not be confounded, as has some-
times been done, with the parts bearing in French
works the same name in the ox, and which are placed
one on each side in a somewhat similar part of the
foot. These, are clearly shown by the structure of
their horny covering, by the presence of bony ele-
ments within, and by comparison with their more
developed condition in other ruminants, to be really
the hoofs of the second and fifth digits, reduced to
a very rudimentary condition.
Besides the ergot there are other patches, more
obvious to ordinary observation, in which the skin is
peculiarly modified from its usual structure. These
are the so-called " chestnuts," or " mallenders " and
'l sallenders " as they are designated in old books.
182 THE STKUCTUEE OF THE HOESE.
They are patches on which no hair grows, but in
which the papillae of the derm or true skin are much
enlarged and covered with an abundant and thick-
ened epidermis, which becomes dry and horny and
sometimes accumulates in considerable quantity on
the surface, occasionally even making a horn-like
projection. Their structure, in fact, is much like
that of a wart or corn, but they are not the results
of pathological changes, though often treated as such
in old works on veterinary surgery. Even so en-
lightened a writer as Youatt includes them among
diseases, and prescribes remedies both external and
internal for the purpose of getting rid of them. They
are, however, perfectly normal structures ; they ex-
ist at birth, are equally developed in both sexes, and
(allowing for certain limited individual variations)
constant in form, size, and position. They consti-
tute, moreover, one of the characteristic distinctions
by which the species JEJquus caballus is distinguished
from the other members of the genus.
They differ in form in the two limbs, but in both
are placed upon the inner surface and nearer the
hinder than the front border. That on the fore limb
is above the carpal or wrist joint ("knee" of the
horse), that on the hind limb below the ankle or
"hock" joint. The former is about two inches long
and three-quarters of an inch wide, pointed at each
THE LIMBS. 183
end, and lying obliquely, so that the long axis has
its lower end directed backwards almost to the pos-
terior border of the limb. When all the loose epi-
dermis which incrnsts it to a variable extent during
life has been removed, the surface is seen to be ele-
vated above the surrounding skin and to have defi-
nite prominent margins, and also to be generally
convex, the tissue of which it is composed being
thicker at the middle than at the edges. The hinder
one is rather smaller and less elevated. Its posterior
margin is nearly straight or regularly convex; its
anterior margin is excavated in its upper third. It
is therefore more pointed above than below. The
upper end is about four inches below the point of
the hock (tuber calcis). The natural color of both is
dark slate, but when much dry epidermis collects on
the surface they have a lighter or yellowish appear-
ance.
In all the species of asses and zebras the hinder
one is absent ; but the one on the fore limb always
exists, although in a modified form. It is broader
or more oval in shape, and with a smoother and
scarcely elevated surface. In the zebra it assumes
the form of a large circular flat black patch of bare
skin, nearly two inches in diameter.
The signification and utility of these structures
are complete puzzles. Various suggestions have
184 THE STRUCTURE OF THE HORSE.
been made, none of which will bear examination.
One of the most plausible, especially in the light of
modern comparative anatomy, is that they are rudi-
ments or vestiges of the inner toe — the thumb or
pollex of the fore limb, the great toe or hallux of the
hind limb — which, as already shown, is not otherwise
represented in the horse. There are, however, many
objections to this theory. The inner toe is always
the first to disappear in all mammals, and no traces
of it are found in any ungulate, either Perissodactyle
or Artiodactyle, except the most ancient forms. It
is, therefore, most unlikely that anything of this
digit should remain in the horse after the complete
disappearance of the second, fourth, and fifth. In
the next place, there is nothing beneath the modified
patch of skin showing any trace of the structure of
a toe, and the resemblance of this patch to a hoof is
of the very slightest character, and, indeed, in the
donkeys and zebras none whatever. But the most
serious objection is the situation of the one that is
most constant — that on the fore limb — where it is
placed, not on the hand, as it would be if it repre-
sented the thumb, but upon the forearm, at some dis-
tance above the wrist- joint. Lastly, such a hypoth-
esis is quite unnecessary, for they obviously belong
to a numerous class of special modifications of par-
ticular parts of the cutaneous surface which occur in
THE LIMBS. 185
very many animals, the use of winch is in most cases
remarkably obscure. Bare spots, thickened patches
or callosities, and tufts of elongated or modified hair,
often associated with groups of peculiar glands, are
very common on various parts of the body, but es-
pecially the limbs, of many ungulates, and to this
category the " chestnuts " of the horse undoubtedly
belong.*
If they teach us nothing else, they afford a valu-
able lesson as to our own ignorance, for if we cannot
guess at the meaning or use of a structure so con-
spicuous to observation, and in an animal whose
mode of life more than any other we have had
the fullest opportunity of becoming intimately ac-
quainted with, how can we be expected to account
off-hand for the endless strange variations of form
or structure which occur among animals whose lives
are passed in situations entirely secluded from hu-
* The apparently capricious distribution of these may be
illustrated by the following diagnoses of two groups or genera
into which the pigmy chevrotains (small deer-like ruminants
with some affinities to pigs) were divided by the late Dr. J.
E. Gray, and which in all other respects closely resemble each
other. (1) Mcminna. "Chin entirely "covered with hair.
Hinder edge of the metatarsus covered with hair, with a large,
smooth, naked prominence on the outer side rather below the
hock." (2) Tragulus. " Throat and chin nakedish, subglan-
dular, with a callous disk between the rami of the lower
jaw, from which a band extends to the fore part of the chin.
Hinder edge of the metatarsus naked and callous."
186 THE STKUCTURE OF THE HOUSE.
man observation, and of whose habits and methods
of existence we know absolutely nothing ?
The Hoofs.
Any one who has read this book so far must be
fully aware by this time that when we speak in or-
dinary language of a horse's " foot," the part we in-
tend to designate is in reality the last joint of its toe.
As the value of the horse to man depends almost
entirely upon its possessing this part in a sound and
healthy state, it is one to which an immense amount
of attention has been paid, and probably no other
structure in the anatomy of any animal has been the
subject of such minute investigation and elaborate
description. It must be confessed that many of the
current accounts of it are almost unintelligible, be-
cause the broad and interesting facts connected with
it are completely obscured by a mass of minute,
tedious, and unnecessary details, which seem to in-
volve a comparatively simple organ in a cloud of
mysterious technicalities. The fact is, that in all its
main component parts, and in their relations to one
another, the last joint of the toe of the horse precisely
resembles that of any other animal, although some
very remarkable and interesting modifications have
taken place, adapting it for the special purpose it has
to play in the economy of the horse.
THE LIMBS. 187
The last segment or "joint" of the human finger
(see Fig. 24, p. 190) differs as much from that of the
horse in the nse to which it is applied as is possible,
yet an examination of its structure will afford a good
key by which to understand the more complex ar-
rangements of the latter. It contains one bone — the
terminal or ungual phalanx. The proximal or up-
per end of this is wide transversely and hollowed
out, fitting by a hinge-joint to the convex surface of
the distal end of the second or middle phalanx of the
digit. The two bones are firmly bound together by
strong ligaments placed on each side of the joint, al-
lowing free movement of flexion and extension, but
not in any other direction. Below the joint the bone
is somewhat constricted, but broadens out again into
a sort of spoon-shaped end. The upper or dorsal
surface is convex, the under or palmar surface flat.
The ends of two tendons, which are worked by mus-
cles situated a long way up in the limb, are fixed, one
on the upper and the other on the under surface of
the bone, and by their alternating contractions and
relaxations cause it, with the structures around, to
move in either direction on its hing'e-like articulation.
Between the bone and the skin are various soft struc-
tures, the terminations of arteries, veins, lymphatics,
and nerves, embedded in a web of cellular or areolar
fibrous tissue, with a considerable amount of fat. of
188 THE STEUCTUEE OF THE HOESE.
which there is a special accumulation, forming a
rounded pad, on the under surface of the end of the
finger, called the bulb. In the skin over this part
the sense of touch is especially developed.
The external surface is completely covered with
a general continuation of the skin of the rest of the
limb, the structure of which has been briefly de-
scribed at p. 176. A part of this covering has, how-
ever, undergone a special modification to form the
nail, which is a hard protecting shield for the most
exposed part of the finger, and the freely-projecting
edge of which serves many useful purposes. The
nail is nothing more than a flattened plate of dry,
hard, and horn-like epidermis, growing from a semi-
lunar groove in the derm and from a depressed sur-
face in front of this. This surface is covered, for the
purpose of increasing its area, with slightly raised
parallel longitudinal rows of papilla?, indications of
which may be seen in the longitudinal ridges with
which the surfaces of most nails are marked. The
nail continually grows at the base and from its in-
ner attached surf ace by the exudation of fresh epi-
dermic material, which pushes forward the older-
formed portion. This, if left to nature, eventually
wears or breaks away at the free edge. The portion
of the derm from which the nail grows is called the
" matrix." The nail of the human hand is, generally
THE LIMBS. 189
speaking, flat, but its surface lias a considerable
curve from side to side, and also, though in a less
degree, in its long diameter.
In those animals which belong to the typically
unguiculated or clawed groups the bone of the last
phalanx is long, but compressed from side to side,
curved, and pointed, and the two sides of the nail
bend completely round, so that their edges nearly
meet at the middle line of the back or under surface
of the finger or toe. In this way the nail becomes
converted into a claw, which forms a sheath sur-
rounding the bone. Usually, however, especially
near the base, the edges do not quite meet, and there
is a groove between them, filled up by softer epi-
dermic material. As it is important for the due ful-
fillment of the function of claws that they should
not be blunted by contact with the ground in walk-
ing, they are, in their most perfect condition, raised
at their ends, the toes resting on bare cushions or
pads placed beneath the joint between the middle
and ungual phalanx.
When the horny covering of the last phalanx is
modified into a hoof, on which the ^animal habitually
rests and walks, the bone is generally broader and
shorter, and the nail is curled round into the form
of a short cylinder obliquely truncated, but with its
edges not meeting behind, and with the interval filled
190
THE STRUCTURE OF THE HORSE.
by a mass of epidermis of great thickness but some-
what softer structure than the nail proper, which is
distinguished as the " sole " of the hoof. This corre-
sponds in position to the rounded end of the human
finger.
1
8
■ m
-19
%\^
Fig. 24. — Section of the finger of man. 1, metacar-
pal bone ; 2, first phalanx ; 3, second phalanx ; 4,
third or ungual phalanx; 7, tendon of extensor
muscle ; 8, tendon of superficial flexor (flexor per-
foratus) ; 9, tendon of deep flexor (flexor per for an s) ;
11 and 14, derm or true skin ; 15, nail ; 17, fibro-
fatty cushion of end of finger ; 18, ditto of palm
behind metacarpophalangeal joint ; 19, thickened
epidermal covering of the same. The corresponding
parts of Figs. 24 and 25 have the same numbers.
THE LIMBS.
191
These three principal modifications of the same
structures, described respectively as nails, claws, and
lo-
■^
I* n
Fig. 25. — Section of the foot of horse. 1, metacarpal
bone ; 2, first phalanx ; 3, second phalanx ; 4, third
or ungual phalanx ; 5, one of the upper sesamoid
bones ; 6, lower sesamoid or "navicular" bone ; 7,
tendon of extensor muscle ; 8, tendon of superficial
flexor {flexor perforatiis) ; 9, tendon of deep flexor
(flexor perforans) ; 10, short flexor or suspensory-
ligament of the fetlock ; 11, derm or true skin, con-
tinued into 12, coronary cushion; 13, lamina! , and
14, villous portions of the hoof matrix ; 15, hoof ;
16, the "heel"; 17, plantar cushion; 18, fibro-
fatty cushion of the fetlock ; 19, bare patch with
thickened epidermal covering or "spur." The cor-
responding parts of Figs. 24 and 25 have the same
numbers.
192 THE STEUCTUEE OF THE HOESE.
hoofs, are met with throughout the Mammalian class,
with numerous varieties or modifications of each,
and transitional conditions by which they pass one
into the other.
The horse shows the most extreme development
of size and perfection of structure to which the hoof
has attained, even considerably exceeding in this re-
spect his nearest living allies, the asses and zebras.
The bone which constitutes its support resembles
that of man in the way it is jointed on to the bone
above by a transversely extended concavity, and in
having the ends of the long tendons of an extensor
and flexor muscle inserted into it, one on the anterior
and one on the posterior surface ; but the bone is
wonderfully different in shape, being very short,
greatly expanded laterally, and ending below in a
sharp but wide, nearly semicircular, distal edge. The
bone is remarkable for its dense, almost ivory-like
character, and is channeled and perforated to allow
the passage of blood-vessels. The presence of a large
sesamoid bone (the "navicular" of veterinarians)
behind the articulation between the middle and dis-
tal phalanges is related to the great development of
these bones, and to increasing the mechanical advan-
tage of the flexor tendon which passes over it. Al-
though not present in most mammals, it is not
peculiar to the horse, being found, though on a
THE LIMBS. 193
smaller scale, in other Perissodactyles. Not only is
the ungual phalanx larger, or at all events broader
in proportion to the rest of the digit, than in any
other mammal, but the parts around it are increased
to a still greater ratio, in order to give that firm basis
of support necessary when only a single toe reaches
the ground. In addition to its breadth, the toe is
prolonged backwards on each side into rounded
prominences with a deep indentation between them,
called the " heels " of the foot, as in comparing the
toe of the horse to the entire human foot they occupy
much the same position as the heel of the latter,
though, of course, they are in reality totally different
parts. In order to provide a support for this enlarge-
ment, the internal framework consists, in addition to
the bones, of certain accessory parts — viz., a. pair of
fibro- cartilaginous masses, called the "lateral carti-
lages," one attached to each side or wing of the un-
gual phalanx and extending backwards towards the
heel, and a large elastic fibro-cellular and adipose
"plantar cushion" (Fig. 25, 17), occupying all the
median region below and behind the bone. The
former have nothing corresponding to them in man,
but the latter agrees in position and structure to the
fibro-fatty cushion of the bulb at the end of the hu-
man finger (Fig. 24, 17).
In the horse this " plantar cushion " is of great
194 THE STRUCTURE OF THE HORSE.
size and importance. It is wedge-shaped ; the nar-
row, pointed end, which is turned forwards and
reaches to the middle of the under surface of the
foot, causes the median triangular prominence called
the " frog." Posteriorly in the middle line is a deep
depression (the " median lacuna"), bounded on each
side by the ''branches of the frog," which end in
rounded projections, the "glomes of the frog" form-
ing the lower part of the heels. Blood-vessels,
nerves, lymphatics, and connective tissue make up
the rest of the structure of the toe, and the whole is
incased in a prolongation of the ordinary skin of the
limb, which, however, has undergone some very con-
siderable modifications. At a sharply defined hue
(the " coronet ") which runs all round the foot, high-
est in front and becoming lower behind, where it
drops rather below the most prominent part of the
heels and dips into the lacuna, the hairy covering
altogether ceases, and a very thick epidermis takes
its place, completely incasing the whole terminal
part of the digit, as a thimble upon the end of a fin-
ger. In order to provide for the nutrition and con-
tinuous growth of this abundant epidermic covering,
the derm has acquired a greatly modified condition,
being very thick and vascular, and its surface is
everywhere immensely increased by folds, ridges,
papilla?, or villi. This vascular and sensitive struct-
THE LIMBS. 195
ure, the " matrix of tlie hoof/7 " subcorneous integu-
ment," or " keratogenous membrane/' as it has been
called, may be divided into three portions, differing
in position and structure :
1. A rounded, prominent ridge (" coronary cush-
ion"), convex from above downwards (Fig. 25, 12),
constitutes the upper edge of the hoof-matrix, im-
mediately contiguous to the hairy skin. It encircles
the front and side of the toe, descending on each side
behind and becoming continuous with the promi-
nences called respectively the glomes, branches, and
body of the frog. Its surface is everywhere covered
with numerous and well-developed little thread-like
prolongations, which, if it is placed in water, float
out, and give the surface a velvety appearance. These
papilla? fit into corresponding tubular depressions in
the epidermic covering. From the coronary cushion
the base of the " wall " of the hoof (to be hereafter
described) grows; it therefore exactly corresponds
to that portion of the matrix of the human nail
which forms the bottom of the semilunar groove.
2. Below this, and separated from it by a narrow
whitish band, the membrane has a very different ap-
pearance. It closely covers the front and sides of
the bone as far as its lower margin, and posteriorly
on each side is continued round the hinder border of
each of the lateral wings, and turns forward to reach
196 THE STKUCTUKE OF THE HOESE.
almost the center of the under surface of the toe at
the apex of the plantar cushion or frog*. This part
of the hoof -matrix (Fig. 25, 13), which from its
structure is called the " podophyllous " or "lamina!"
tissue, is deeper from above downwards in front, and
gradually gets shallower posteriorly, the incurved
ends (which correspond to the " bars " of the horny
hoof) thinning almost to nothing at their termina-
tions. Instead of being covered with irregularly-
scattered villi, like the coronary cushion and frog, its
surface is raised into very numerous (five or six hun-
dred altogether) longitudinal, parallel, fine leaf -like
ridges or "lamella?," all extremely vascular and sen-
sitive, and being themselves covered on each side
with numerous other finer ridges, set obliquely upon
them — a most complex and delicate apparatus, enor-
mously increasing the superficial area of the kerato-
genous membrane. This region of the matrix of the
horse's hoof corresponds to the flat surface below the
human nail, and the longitudinal ridges observed in
the latter are obviously the same structures as the
lamella? of the horse's foot, only in a very slightly
developed condition.
3. The third part of the matrix of the hoof is that
portion of the vascular derm which covers the lower
surface of the pedal bone, or the " sole " of the foot.
It is crescentic in shape, and bordered all round by
THE LIMBS. 197
the lower edge of the lamallar tissue. This, like the
first, has a fine villous surface. The great size of
this region is one of the peculiarities of the horse's
foot. The covering of the sole is continuous pos-
teriorly with that of the plantar cushion, which has
also a villous surface.
Over the whole of this soft, sensitive, and highly
vascular derm is, as before said, a very thick epider-
mic layer, which is distinguished by the name of
" hoof." Oue of the properties of the horny material
of which this is composed, which specially fits it for
the function it has to perform, is that it is a non-
conductor of heat. It is also moderately hard, tough,
and elastic, and, like all epidermic structures, not
sensitive itself, though it will transmit impressions
through its tissue to the sensitive structures below.
From the foot of the dead animal the hoof may
be removed entire by maceration or by immersion in
hot water, when it will be seen to form a hollow box
or case of somewhat complex form, its inner surface
being exactly moulded on the parts around which it
grows. Its general shape is that of an obliquely
truncated cone, considerably higher in front than be-
hind. As in the vascular surface beneath it, several
distinct portions or regions can be distinguished.
The densest and most important part is the " wall "
or " crust," which exactly corresponds to the whole
198 THE STRUCTURE OF THE HORSE.
of the human nail, though differing in its much
greater thickness and in the sides being not only
greatly prolonged backwards, but also sharply bent
inwards and forwards, forming the " bars " (Fig. 26,
5 and 6). The upper edge of the wall is hollowed to
fit on to the coronary cushion. The inner surface
is longitudinally furrowed by deep and complex
grooves, which exactly correspond to the delicate
lamellae and laminellae of the " podophyllous tissue."
The new hoof continually grows from the coronary
cushion above, and slides down over the lamellae of
the derm, receiving from them upon its inner side a
certain amount of addition to its thickness in the
form of soft epidermic cells, which afterwards harden
and become incorporated in the general mass. The
external surface of the wall when in a natural con-
dition is smooth and shining, and appears to be made
up of fine, closely arranged, parallel fibers, passing
in a straight hue from the upper to the lower mar-
gin. There are also not unfrequently transverse
grooves or rings, indicating varying conditions of
the matrix at the time of growth, especially marked
in certain abnormal states of health.
The different regions of the wall have received
technical names useful for descriptive purposes. The
front part is called the " toe " (Fig. 26, 2, 3) ; the two
sides, the outer and inner " quarters " (1,2, and 4, 3) ;
THE LIMBS.
199
the points where the wall suddenly bends inwards
and forwards, the " buttresses" (1 and 4) • the inner
reflected ends, which nearly reach the center of the
sole, the "bars" (5 and 6).
/>4v
__ 6
-Z,
Fig. 26. — Under surface of hoof of horse (from Lei-
sering). 1, 2, 3, and 4, the wall ; the part be-
tween 2 and 3 being the toe ; between 1 and 2,
and 4 and 3, the outside and inside quarters ; 1 and
4, the buttresses or angles of inflection of the wall
to form the bars, 5 and 6 ; 7, the sole ; 8, the point
of the frog ; 9 and 10, the branches of the frog ;
11 and 12, the lateral lacunae ; 13, the median la-
cuna ; 14, the heels.
The space between the lower edges of the wall is
filled up in front by a flat or rather concave plate of
a crescentic shape, called the " sole " (7), composed
of softer and less fibrous material than the wall. Its
14
200 THE STRUCTURE OF THE HORSE,
anterior and lateral Inn-dors, where it comes in con-
tact with the inner surface of the toe and quarters of
the wall, form nearly two-thirds of a circle. Its pos-
terior concave border is bounded on each side by the
bars, and in the middle it is deeply notched to receive
the point of the frog1.
Lastly, all the posterior part of the foot which
comes to the 'ground is formed by the frog: (8, 0,
and lib and its posterior prolongations, called the
"branches" and "glomes." covered by a thick, cal-
lous, but not very horny epidermis, and which cor-
responds in form with that of the under surface
of the "plantar" cushion previously described. We
can distinguish a pyramidal median prominence (8),
pointed in front where it reaches the center of the
sole, with a groove on each side separating: it from
the bars, called the "lateral lacuna" ^11 and 12) ; a
deeper groove in the middle line farther back, the
-median lacuna" (13), on each side of which are the
branches of the frog, which posteriorly are swollen
out into the glomes, rounded prominences forming
the lower part of the heels (14), and continued round
on each side of the hoof into the coronary cushion.
The terminal portions of the horse's four limbs are
remarkably alike both in external appearance and
internal structure, more so than are those of aoy
other animal ; and yet close inspection will show
THE LIMBS. 201
differences by which they can be distinguished by a
practiced eye. The hoofs of the fore feet are broader
and rounder in front, those of the hind feet narrower
and more pointed. The right and left hoofs of either
limb can be distinguished by observing that the in-
ner edge of the wall is ilatter and the outer more
convex.
It will now be clearly seeL that, in comparing the
under surface of the horse's foot with the tip of the
human finger, the free or lower edge of the; wall of
the former corresponds with the free edge of the nail
of the latter, only vastly more developed in extent, in
complexity of involution, and in thickness ; the frog
and all its accessory parts to the rounded free tip and
bulb of the finger, also greatly developed, so as to
form the heel-like projection so essential to give sta-
bility to the horse's foot in standing; while the sole
is only represented by the thin curved line between
the under surface of the nail and the skin covering
the tip of the finger.
Comparing the horse's toe with that of a clawed
animal — a dog or cat, for instance — the wall of the
hoof represents the horny sides of the claw; the sole
the narrow soft under surface of the claw, where the
edges do not meet ; the frog and its branches and
glomes the smaller oval bare pad under the toe;
while the ergot or bare space behind the fetlock-joint
202 THE STRUCTURE OF THE HORSE.
represents (as shown before) the large pad under the
middle of the foot.
The hoofs of asses and zebras, though formed on
exactly the same general plan as those of the horse,
differ in being smaller, and especially narrower. The
different parts of the inferior surface, the wall and
bars, the sole and the frog, can be made out, though
they are less distinctly marked from each other than
in the horse.
The mechanical arrangement of the under sur-
face of the horse's hoof in its natural state is admi-
rably adapted to the purpose it has to fulfill. The
different varieties of horny tissue of which it is com-
posed and their complex arrangement recall those of
the grinding-surface of the molar teeth. The wall
or crust, completely encircling the front and sides,
and reflected inwards and forwards almost to the
center, being composed of a harder and more resist-
ing material than the rest, like the enamel of the
teeth, always stands out as a ridge beyond the other
structures, and not only bears the principal weight,
but prevents the tendency to slip which a uniformly
smooth surface would have. The sole is more or less
concave, being less dense and its surface exfoliating
more readily than the other parts, but it comes in
contact with the ground when this is of a soft
and yielding nature. The projections formed by the
THE LIMBS. 203
elastic plantar cushion, covered by the horny frog
and its backward prolongations, also bear much of
the weight when these parts are left in their natural
condition, though the ease with which they yield to
the paring-knife offers a temptation which farriers
seem rarely able to resist, much to the detriment of
the proper action of the horse's foot.
In a state of nature, when the animal is free to
choose the ground it runs over, the wear of the hoof
is in exact proportion to its growth, and the organ
always maintains itself in perfect condition. If,
however, the horse is confined to ground so soft that
only insufficient abrasion of the free surface of the
hoofs can take place, they grow to an abnormal
length. Horses turned out in the Falkland Islands,
where the whole of the surface of the land Consists
of soft, moist, mossy bog, often have hoofs nearly a
foot in length, bending and curling up in various di-
rections, so that the animal at last can scarcely stand
upon them. On the other hand, horses that are kept
at work upon artificially hardened roads wear their
hoofs so much faster than they grow, that from time
immemorial their masters have found it necessary to
protect them with some kind of artificial covering.
Hence the almost universal use of iron shoes for
horses in a state of domestication. Unfortunately,
the subject of horse-shoeing has been too long left in
204 THE STRUCTURE OF THE HORSE.
the hands of ignorant mechanics, by whose obstinate
adhesion to routine and ancient custom all the at-
tempts of those who have endeavored to introduce a
more rational system are constantly foiled. This
subject, however, though of immense practical im-
portance, is beyond the domain of natural history,
except in so far that a knowledge of the structure and
action of the foot in its natural state ought to be a
guide to those whose duty it is to counteract the un-
natural conditions to which we subject it .*
* Among many other works, see a small pamphlet on The
Structure of the Horse's Foot, and the Principles of Shoeing, by-
Prof. G. T. Brown, C.B., reprinted from the Journal of the
Royal Agricultural Society of England (1888), and the larger
work of Dr. George Fleming, C.B. on Horse Shoes and Horse
Shoeing, 1889.
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