The even-toed ungulates form the mammal order Artiodactyla. They are ungulates whose weight is borne (if they've more than two toes) about equally by the third and fourth toes, rather than mostly or entirely by the third as in perissodactyls. Another key distinguishing feature is the shape of the astragalus (a bone in the hock joint), which has a double-pulley structure in artiodactyls, giving the foot greater flexibility. There are about 220 artiodactyl species, including many that are of grea… (More on Artiodactyl)