, the canines are
also left; the molars and premolars are practically alike in all recent
species, and in all of which we know the soft parts, the stomach has but
one compartment, and there is an enormous caecum. It is probable that
they took rise earlier than their split-footed relations, and their
Tertiary remains are far more numerous, but their tendency is toward
disappearance, and among existing mammals they are represented only by
horses, asses, rhinoceroses, and tapirs.

Contrasted with these, _Artiodactyla_ have always an even number of
functional digits, the third and fourth reaching the ground
symmetrically, bearing the weight and forming the "split hoof;" the
second and fifth remain, in most cases, as mere vestiges, showing
externally as the accessory hoofs or dewclaws; in the hippopotamus alone
they are fully developed and the animal has a four-toed foot. In deer
and bovine animals the incisors and frequently the canines have
disappeared from the upper jaw, and the molars are unlike the premolars
in having two lobes instead of one. The stomach is always more or less
complex; at its extreme reaching the ruminant type with four
compartments, in association with which is a caecum reduced in size and
simple in form. Nearly all have horns or antlers, at least in one sex.

Most split-hoofed animals are ruminants, but there is a small remnant,
probably of early types, which are not. The present ungulates may be
summed up in this way:

Odd-toed: _(Perissodactyla)_--
Horse,
Ass,
Rhinoceros,
Tapir.

Even-toed: _(Artiodactyla)_--

Non-ruminants--
Hippopotamus,
Swine,
Peccaries.

Ruminants--
Camels, Llamas,
Chevrotains,
Giraffe,
Antelopes,
Sheep, Goats,
Musk-ox,
Oxen,
Deer.

The non-ruminant artiodactyls need not detain us long. Hippopotamuses
are little more than large pigs with four toes; they were never
American, though many species, some very small, are found in the
European Tertiary. The two existing species are African.

In the western hemisphere swine are represented by the peccaries,
differing from them chiefly in having six less teeth, one less accessory
toe on the hind foot, and in a stomach of more complex character.
Peccaries also have the metapodial bones supporting the two functional
digits fused together at their upper ends, forming an imperfect "cannon
bone," which is a characteristic of practically all the ruminants, but
of no other hoofed beasts. One species only enters t