=Horse and Man Compared= (Figs. 381, 399).--To which finger and toe on man’s hand and foot does the toe of a horse’s foot correspond? 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? Does the most elongated part of the fore foot correspond to the finger, palm, or wrist? On the hind foot is it toe, instep, or ankle? Is the fetlock at the toe, instep, or heel? (Fig. 385.) Is the hock at the toe, instep, heel, or knee? _Order_ ____. _Why?_ ____. [Illustration: FIG. 381.--Left leg of man, left hind leg of dog and horse; homologous parts lettered alike.] =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.] 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: _Equus_ _Protohippus_ _Pliohippus_ _Miohippus_ _Mesohippus_ _Orohippus_ FIG. 383.--Feet of the ancestors of the horse.] [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.]