telligent than those of
our day.

It would require volumes to trace the history of the growth of these
early mammals, and show how they, step by step, came to their present
higher state. We will take only one of the simplest of these changes,
which happens to be also the one which we know best. This is the
change that led to the making of our common horses, which seem to have
been brought into life on the continent of North America. The most
singular thing about our horses is that the feet have but one large
toe or finger, the hoof, the hard covering of which is the nail of
that extremity. Now it seems hard to turn the weak, five-fingered
feet of the animals of the lower Tertiary--feet which seem to be
better fitted for tree-climbing than anything else--into feet such as
we find in the horse. Yet the change is brought about by easy stages
that lead the successive creatures from the weak and loose-jointed
foot of the ancient forms to the solid, single-fingered horse's hoof,
which is wonderfully well-fitted for carrying a large beast at a swift
speed, and is so strong a weapon of defence that an active donkey can
kill a lion with a well-delivered kick.

[Illustration: FIG. 10. FEET OF TERTIARY MAMMALS.]

The oldest of these creatures that lead to the horses is called
_Eohippus_ or beginning horse. This fellow had on the forefeet four
large toes, each with a small hoof and fifth imperfect one, which
answered to the thumb. The hind feet had gone further in the change,
for they each had but three toes, each with hoofs, the middle-toed
hoof larger and longer than the others. A little later toward our day
we find another advance in the _Orohippus_, when the little imperfect
thumb has disappeared, and there are only four toes on the forefeet
and three on the hind.

Yet later we have the _Mesohippus_ or half-way horse. There are still
three toes on the hind foot, but one more of the fingers of the
forefeet has disappeared. This time it is the little finger that goes,
leaving only a small bone to show that its going was by a slow
shrinking. The creature now has three little hoofs on each of its
feet.

Still nearer our own time comes the _Miohippus_, which shows the two
side hoofs on each foot shrinking up so that they do not touch the
ground, but they still bear little hoofs. Lastly, about the time of
man's coming on the earth, appears his faithful servant, the horse, in
which those little side hoofs have disappeared, leav