sia. The rhinoceros has had a long
and interesting history. From the primitive Hyrochinus of the Eocene, in
which it is dimly foreshadowed, we pass to a large and varied family
in the later periods. In the Oligocene it spreads into three great
branches, adapted, respectively, to life on the elevated lands, the
lowlands, and the water. The upland type (Hyracodon) was a light-limbed
running animal, well illustrating the close relation to the horse. The
aquatic representative (Metamynodon) was a stumpy and bulky animal.
The intermediate lowland type was probably the ancestor of the modern
animal. All three forms were yet hornless. In the Miocene the lowland
type (Leptaceratherium, Aceratherium, etc.) develops vigorously, while
the other branches die. The European types now have two horns, and in
one of the American species (Diceratherium) we see a commencement of
the horny growths from the skull. We shall see later that the rhinoceros
continued in Europe even during the severe conditions of the glacial
period, in a branch that developed a woolly coat.

There were also in the early Tertiary several sidebranches of the
horse-tapir-rhinoceros family. The Palaeotheres were more or less
between the horse and the tapir in structure; the Anoplotheres between
the tapir and the ruminant. A third doomed branch, the Titanotheres,
flourished vigorously for a time, and begot some strange and monstrous
forms (Brontops, Titanops, etc.). In the larger specimens the body was
about fourteen feet long, and stood ten feet from the ground. The long,
low skull had a pair of horns over the snout. They perished like the
equally powerful but equally sluggish and stupid Deinocerata. The
Tertiary was an age of brain rather than of brawn. As compared with
their early Tertiary representatives' some of our modern mammals have
increased seven or eight-fold in brain-capacity.

While the horses and tapirs and rhinoceroses were being gradually
evolved from the primitive types, the Artiodactyl branch of the
Ungulates--the pigs, deer, oxen, etc.--were also developing. We must
dismiss them briefly. We saw that the primitive herbivores divided early
in the Eocene into the "odd-toed" and "even-toed" varieties; the name
refers, it will be remembered, not to the number of toes, but to the
axis of stress. The Artiodactyl group must have quickly branched in
turn, as we find very primitive hogs and camels before the end of the
Eocene. The first hog-like creature (H