=Hoofed Mammals.=—All the animals in this order walk on the tips of their toes, which have been adapted to this use by the claws having developed into _hoofs_. The order is subdivided into the _odd-toed_ (such as the horse with one toe and the rhinoceros with three) and the _even-toed_ (as the ox with two toes and the pig with four). All the even-toed forms except the pig and hippopotamus chew the cud and are given the name of _ruminants_. [Illustration: FIG. 381.—Left leg of man, left hind leg of dog and horse; homologous parts lettered alike. ] =Horse and Man Compared.=—To which finger and toe on man’s hand and foot does a horse’s foot correspond? (Figs. 381, 383, 399.) Has the horse kneecaps? Is its heel bone large or small? Is the fetlock on toe, instep, or ankle? Does the part of a horse’s hind leg that is most elongated correspond to the thigh, calf, or foot in man? On the fore leg, is the elongated part the upper arm, forearm, or hand? (Figs. 395, 399.) Does the most elongated part of the fore foot correspond to the finger, the palm, or the wrist? (Fig. 382.) On the hind foot is it toe, instep, or ankle? Is the fore fetlock on the finger, the palm, or the wrist? (Figs. 382, 385, 399.) Is the hock at the toe, the instep, the heel, or the knee? =Specializations of the Mammals.=—The early mammals, of which the present marsupials are believed to be typical, had five toes provided with claws. They were not very rapid in motion nor dangerous in fight, and probably ate both animal and vegetable food. [Illustration: FIG. 382.—SKELETONS OF FEET OF MAMMALS. _P_, horse; _D_, dolphin; _E_, elephant; _A_, monkey; _T_, tiger; _O_, aurochs; _F_, sloth; _M_, mole. =Question=: Explain how each is adapted to its specialized function. ] [Illustration: FIG. 383.—Feet of the ancestors of the horse. ] According to the usual rule, they tended to increase faster than the food supply, and there were continual contests for food. Those whose claws and teeth were sharper drove the others from the food, or preyed upon them. Thus the specialization into the bold flesh eating beasts of prey and the timid vegetable feeders began. Which of the flesh eaters has already been studied at length? The insectivora escaped their enemies and found food by learning to burrow or fly. The rodents accomplished the same result either by acquiring great agility in climbing, or by living in holes, or by running. The proboscidians acquired enormous size and strength. The hoofed animals found safety in flight. [Illustration: FIG. 384.—TAPIR OF SOUTH AMERICA (_Tapirus americanus_). × ¹⁄₂₅. =Questions=: How does it resemble an elephant? (Fig. 376.) A horse? (p. 210.) ] [Illustration: FIG. 385.—HORSE, descended from a small wild species still found in Western Asia. ]