Coming now to the ruminants, all digits except the third and fourth have disappeared from camels and llamas, and the nails on these are limited to their upper surface without forming a hoof, the under side being a broad pad, upon which they tread. No camel-like beasts have inhabited North America since the Pliocene age. Chevrotains, or muis deer (_Tragulidae_), are not deer in any true sense, as they have but three compartments to the stomach; antlers are absent and in their place large and protruding canine teeth are developed in the upper jaw, and the lateral metacarpal bones are complete throughout their length, instead of being represented by a mere remnant. They are the smallest of ungulates, and inhabit only portions of the Indo-Malayan region. Camels also have upper canines, and the outer, upper incisors as well. The giraffe is separated from all living ungulates by the primitive character of its so-called "horns," which are not horns in the usual sense, but simply bony prominences of the skull covered with hair. Some of the earliest deer-like animals seem to have had simple or slightly branched antlers which were not shed, and which there is reason to believe were also hairy, and in these, as well as in other characters, giraffes and the early deer may not have been far apart. The "okapi," Sir Harry Johnston's late discovery in the Uganda forests, seems to have come from the same ancestral stock, but the giraffe has no other existing relatives. The true deer, to which we shall return, are readily enough distinguished from the ox tribe and its allies by their solid and more or less branched antlers, usually confined to males, and periodically shed. So, through this rapid survey, we have dropped out of the hoofed beasts all but the bovines and their near allies, and are thus far advanced toward our definition of a bison, but from this point we shall not find it easy to draw sharp distinctions, for while the _Bovidae_, as a whole, are well enough distinguished from all other animals, their characteristics are so much mixed among themselves that it is hardly possible to find any one or more striking features peculiar to one group, and for most of them recourse must be had to associations of a number of lesser characters. Oxen, antelopes, sheep and goats agree in having hollow horns of material similar to that of which hair and nails are formed, permanently fixed upon the skull in all but one species; none of them have more than the two middle digits functionally developed, one on each side of the axis of the leg; none have the lower ends remaining of the meta-podial bones belonging to the two accessory digits; and none have either incisor or canine teeth in the upper jaw.