All the Artiodactyla are strictly terrestrial, none being arboreal in their habits. The Hippopotamus is the only member of the group which is aquatic, spending much of its life in the water, without, however, any special modification of its limbs or tail like that found in the more truly aquatic Seals, Sirenia, or Whales.
There is a great uniformity throughout the order in the general plan upon which the limbs are constructed. In all the species the wrist in the fore limb—commonly called the knee—and the heel in the hind limb—the hock—is raised a considerable distance above the ground, at the same time that the whole weight of the body is carried upon the extreme tips of the toes, the terminal bones of which are expanded within the hoof to increase the basis of support. The collar-bone is absent in all, as it is in nearly every animal that does not use its fore limbs for any other purpose than that of carrying the weight of the front parts of its body.
In the Perissodactylate Rhinoceros the horn or horns is or are situated in the middle line of the face above the nose, and are not supported upon any bony horn core. In all those Artiodactyla which carry horns or antlers, there are appendages paired and lateral in position, at the same time that they are either supported upon bony cores, or are formed of bone itself, and are situated upon the forehead.
The following table best represents our present knowledge as to the classification of the Artiodactyla:—
| ORDER UNGULATA |  | SUB-ORDER ARTIODACTYLA |  | Non-ruminants. | | Pigs of the Old World. |
| Peccaries of the New World. | ||||||
| Hippopotami. | ||||||
| Ruminants. |  | Camels. | ||||
| Llamas. | ||||||
| Chevrotains or Deerlets. | ||||||
| Bovidæe (Oxen). | ||||||
| Cervidæ (Deer). |
A. H. GARROD.
I.—SUIDÆ, OR HOG FAMILY.
THE Non-Ruminantia, or Artiodactyls which do not chew the cud, possess the following characters: they usually have more than one pair of incisors in the upper jaw, they are devoid of horns, and the stomach has rarely more than two divisions. In only one genus, that of the Peccary, are the metatarsal and metacarpal bones united into one compact bony mass. They are divisible—as the above table indicates—into three families: the Suidæ, or Hogs, the Hippopotamidæ, or Hippopotamuses, and the Anoplotheridæ,[269] or Anoplotheres, an extinct family, met with only in the Eocene strata of the Old and New Worlds.
The Hog family may be divided into three well-marked groups:—1, the True Swine, consisting of three genera, Sus, Potamochœrus, and Babirusa; 2, the Wart Hogs, represented by one genus, Phacochœrus; and 3, the Peccaries, represented also by one genus, Dicotyles. They have three kinds of teeth—incisors, canines, and boss-covered or transversely ridged grinders—slender limbs, and the third and fourth toes are considerably larger than the second and fifth.