Order Perissodactyla
摘要
The order Perissodactyla includes horses, donkeys, and tapirs that are characterized by unguligrade limbs; third digit of each front and hindfoot larger than the others, in symmetry with the axis; digits usually one or four in the fore or hind feet; femur with a third trochanter; astragals with a pulley-like surface dorsally and flattened underneath. Distribution nearly cosmopolitan. Two suborders, Ceratomorpha and Hippomorpha, each with one family, Tapiridae and Equidae (introduced), occur in North America.