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the succession of living forms which is presented to us by
fossil remains。
Those who have attended to the progress of palaeontology are
aware that evidence of the character which I have defined has
been produced in considerable and continually…increasing
quantity during the last few years。 Indeed； the amount and the
satisfactory nature of that evidence are somewhat surprising；
when we consider the conditions under which alone we can hope to
obtain it。
It is obviously useless to seek for such evidence except in
localities in which the physical conditions have been such as to
permit of the deposit of an unbroken； or but rarely interrupted；
series of strata through a long period of time； in which the
group of animals to be investigated has existed in such
abundance as to furnish the requisite supply of remains； and in
which； finally； the materials composing the strata are such as
to ensure the preservation of these remains in a tolerably
perfect and undisturbed state。
It so happens that the case which； at present； most nearly
fulfils all these conditions is that of the series of extinct
animals which culminates in the horses； by which term I mean to
denote not merely the domestic animals with which we are all so
well acquainted； but their allies； the ass； zebra； quagga； and
the like。 In short； I use 〃horses〃 as the equivalent of the
technical name Equidae； which is applied to the whole
group of existing equine animals。
The horse is in many ways a remarkable animal； not least so in
the fact that it presents us with an example of one of the most
perfect pieces of machinery in the living world。 In truth； among
the works of human ingenuity it cannot be said that there is any
locomotive so perfectly adapted to its purposes； doing so much
work with so small a quantity of fuel； as this machine of
nature's manufacturethe horse。 And； as a necessary consequence
of any sort of perfection； of mechanical perfection as of
others； you find that the horse is a beautiful creature； one of
the most beautiful of all land…animals。 Look at the perfect
balance of its form； and the rhythm and force of its action。
The locomotive machinery is； as you are aware； resident in its
slender fore and hind limbs； they are flexible and elastic
levers； capable of being moved by very powerful muscles； and； in
order to supply the engines which work these levers with the
force which they expend； the horse is provided with a very
perfect apparatus for grinding its food and extracting therefrom
the requisite fuel。
Without attempting to take you very far into the region of
osteological detail； I must nevertheless trouble you with some
statements respecting the anatomical structure of the horse；
and； more especially； will it be needful to obtain a general
conception of the structure of its fore and hind limbs； and of
its teeth。 But I shall only touch upon those points which are
absolutely essential to our inquiry。
Let us turn in the first place to the fore…limb。 In most
quadrupeds； as in ourselves； the fore…arm contains distinct
bones called the radius and the ulna。 The corresponding region
in the horse seems at first to possess but one bone。 Careful
observation； however； enables us to distinguish in this bone a
part which clearly answers to the upper end of the ulna。 This is
closely united with the chief mass of the bone which represents
the radius； and runs out into a slender shaft which may be
traced for some distance downwards upon the back of the radius；
and then in most cases thins out and vanishes。 It takes still
more trouble to make sure of what is nevertheless the fact； that
a small part of the lower end of the bone of the horse's fore
arm； which is only distinct in a very young foal； is really the
lower extremity of the ulna。
What is commonly called the knee of a horse is its wrist。
The 〃cannon bone〃 answers to the middle bone of the five
metacarpal bones； which support the palm of the hand in
ourselves。 The 〃pastern；〃 〃coronary；〃 and 〃coffin〃 bones of
veterinarians answer to the joints of our middle fingers； while
the hoof is simply a greatly enlarged and thickened nail。 But if
what lies below the horse's 〃knee〃 thus corresponds to the
middle finger in ourselves； what has become of the four other
fingers or digits？ We find in the places of the second and
fourth digits only two slender splint…like bones； about two…
thirds as long as the cannon bone； which gradually taper to
their lower ends and bear no finger joints； or； as they are
termed； phalanges。 Sometimes； small bony or gristly nodules are
to be found at the bases of these two metacarpal splints； and it
is probable that these represent rudiments of the first and
fifth toes。 Thus； the part of the horse's skeleton； which
corresponds with that of the human hand； contains one overgrown
middle digit； and at least two imperfect lateral digits； and
these answer； respectively； to the third； the second； and the
fourth fingers in man。
Corresponding modifications are found in the hind limb。
In ourselves； and in most quadrupeds； the leg contains two
distinct bones； a large bone； the tibia； and a smaller and more
slender bone； the fibula。 But； in the horse； the fibula seems；
at first； to be reduced to its upper end； a short slender bone
united with the tibia； and ending in a point below； occupying
its place。 Examination of the lower end of a young foal's shin
bone； however； shows a distinct portion of osseous matter； which
is the lower end of the fibula； so that the apparently single；
lower end of the shin bone is really made up of the coalesced
ends of the tibia and fibula； just as the； apparently single；
lower end of the fore…arm bone is composed of the coalesced
radius and ulna。
The heel of the horse is the part commonly known as the hock。
The hinder cannon bone answers to the middle metatarsal bone of
the human foot； the pastern； coronary； and coffin bones； to the
middle toe bones； the hind hoof to the nail； as in the fore…
foot。 And； as in the fore…foot； there are merely two splints to
represent the second and the fourth toes。 Sometimes a rudiment
of a fifth toe appears to be traceable。
The teeth of a horse are not less peculiar than its limbs。 The
living engine； like all others； must be well stoked if it is to
do its work； and the horse； if it is to make good its wear and
tear； and to exert the enormous amount of force required for its
propulsion； must be well and rapidly fed。 To this end； good
cutting instruments and powerful and lasting crushers are
needful。 Accordingly； the twelve cutting teeth of a horse are
close…set and concentrated in the fore…part of its mouth； like
so many adzes or chisels。 The grinders or molars are large； and
have an extremely complicated structure； being composed of a
number of different substances of unequal hardness。 The
consequence of this is that they wear away at different rates；
and； hence； the surface of each grinder is always as uneven as
that of a good millstone。
I have said that the structure of the grinding teeth is very
complicated； the harder and the softer parts being； as it were；
interlaced with one another。 The result of this is that； as the
tooth wears； the crown presents a peculiar pattern； the nature
of which is not very easily deciphered at first； but which it is
important we should understand clearly。 Each grinding tooth of
the upper jaw has an outer wall so shaped that； on the
worn crown； it exhibits the form of two crescents； one in front
and one behind； with their concave sides turned outwards。 From
the inner side of the front crescent； a crescentic front
ridge passes inwards and backwards； and its inner face
enlarges into a strong longitudinal fold or pillar。
From the front part of the hinder crescent； a back ridge
takes a like direction； and also has its pillar。
The deep interspaces or valleys between these ridges and
the outer wall are filled by bony substance； which is called
cement； and coats the whole tooth。
The pattern of the worn face of each grinding tooth of the lower
jaw is quite different。 It appears to be formed of two crescent…
shaped ridges； the convexities of which are turned outwards。
The free extremity of each crescent has a pillar； and
there is a large double pillar where the two crescents
meet。 The whole structure is； as it were； imbedded in cement；
which fills up the valleys； as in the upper grinders。
If the grinding faces of an upper and of a lower molar of the
same side are applied together； it will be seen that the opposed
ridges are nowhere parallel； but that they frequently cross；
and that thus； in the act of mastication； a hard surface in the
one is constantly applied to a soft surface in the other； and
vice versa。 They thus constitute a grinding apparatus of
great efficiency