All these families, _Felidæ_, _Ursidæ_, _Canidæ_, and _Phocidæ_ form together one greater group or "order," to which, of course, these four families are subordinate. This order is called "_Carnivora_," because it is made up of carnivorous or flesh-eating beasts.
The other familiar beasts first referred to--our domestic cattle of all kinds--form, together with all swine, horses and all asses, deer, antelopes and camels, another great order of beasts called _Ungulata_, because the nails of their feet are so large and solid as to form "hoofs." This order of hoofed-beasts, or ungulates, is a very large order, and is divided into two sub-orders, and in each sub-order are various families containing more or fewer genera.
The two sub-orders are characterized by the structure of the foot. The toes of the hind foot, which are made use of in progression, are even in number in one sub-order and are odd-numbered in the other sub-order.
The sub-order of odd-toed ungulates, or _Perissodactyla_, includes in our day only the horses, asses, zebras, and quaggas (united together in the family _Equidæ_); the tapirs, the rhinoceroses, and the little hyrax--the coney of Scripture. In ancient times, however, this sub-order was a very large one, but the great majority of the forms belonging to it, which formerly lived, have now become extinct.
The sub-order of even-toed ungulates, or _Artiodactyla_, comprises all oxen, sheep, goats, antelopes, giraffes, deer, chevrotains,[10] llamas, and camels. All these, from their practice of "chewing the cud," are called "ruminants," and they are multitudinous in kinds. The great plains of Southern Africa are the special home of most kinds of antelope, and the giraffe is exclusively African. Deer have their head-quarters in Asia, though they exist in South America as well as throughout the Northern Hemisphere.
Besides the ruminating artiodactyles there is also an extensive group of non-ruminating artiodactyles, made up of all the various kinds of swine (including the American peccaries), together with the hippopotamus, now found nowhere but in Africa. Distinct as are the ruminating and non-ruminating artiodactyles now, they were in ancient time connected by a great number of intermediate forms which have utterly passed away.