LESSONS IN ZOOLOGY. 309 



molars. They are natives of Africa and Southern Asia. They 

 have hoofs on the 2d, 3d and 4th toes of each foot. 



The Equidse are as noted for their graceful, slender forms as the 

 other members of the order are for their bulky, clumsy bodies. 

 The dentition is 6 incisors, 2 canines, 8 premolars and 6 molars 

 in each jaw. Each of the incisors has a little pit near the sum- 

 mit, which, filled with foreign matter, seems like a black spot, that 

 wears away with age. This pit is peculiar to horses, and is not 

 found in the teeth of geological ancestors of the horse. The 

 canines are small, conical teeth and are usually present in both 

 jaws only in the male. The knee and hock joints of the horse 

 correspond to the wrist and ankle joints of man, the bones 

 below to the middle bone of the hand, and the bones of the mid- 

 dle finger are represented by the bones below the fetlock joint. 

 The hoof in all the ungulates corresponds with the nails or 

 claws of other animals. The slender form of the horse fits him 

 for harder ground and more open country than that occupied by 

 the tapir and rhinoceros, and his well developed incisors enable 

 him to take different kinds of food. The zebra, wild ass and 

 quaggas belong to the horse family. The present members of the 

 horse family are natives of the Old World, but in comparatively 

 recent geological times there were several species of horses in 

 America. Some of these ancient horses had three and some four 

 toes instead of one, as does the present species. 



The Artiodactyla, are animals with paired hoofs, the third and 

 fourth digits on each foot supporting the body, the second and 

 fifth digits are generally present but are rudimentary and do not 

 help support the body. 



The dorsal and lumbar vertebrae are 19 or 20 ; the premolars 

 are single, while the molars are two-lobed and the other teeth are 

 variable. This order contains several families. 



The Suidse or swine family have an elongated mobile snout, 

 and the skin is clothed with coarse bristles. There are 6 incisors, 

 2 canines, 8 premolars and 6 molars in each jaw, sometimes an 

 upper incisor and a premolar are suppressed. 



The canines in the male are developed into formidable tusks. 



