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
th