418 



GENERAL ZOOLOGY 



muses, pigs, camels, deer, the giraffes, antelopes, oxen, goats, 

 sheep, rhinoceroses, horses, and elephants. All these mam- 

 mals have the toes ending in either a blunt nail or a fully 

 developed hoof, both of which structures are formed from 

 the thickening of the skin of the toes. In ungulates like the 

 cow and sheep there are two divisions in the hoof, and the 

 animals really walk on the tip of the third and fourth dig- 

 its, the others being 

 much reduced in size. 

 In the horse and its 

 allies this reduction 

 has [gone much far- 

 ther, so that the tip 

 only of the third digit 

 is used for support. 

 The elephants have 

 five toes, each incased 

 in a short nail. The 

 living species of ele- 

 phants undoubtedly 

 would have been re- 

 moved to a separate order if fossil forms had not been dis- 

 covered possessing characters intermediate between these 

 mammals and other ungulates. 



Ungulates are adapted to a terrestrial life and feed almost 

 entirely on vegetable food. Four kinds of teeth are present, 

 — incisors, canines, premolars, and molars. The first kind 

 and the last two kinds will be recognized from the study of 

 the squirrel ; the canines, so named because they are well- 

 developed in the dog (Lat. canis, " dog"), fill the space be- 

 tween the incisors and premolars. The canines are often 

 elongated to form tusks for defense or for obtaining food ; 

 the incisors serve to crop the herbage ; the molars and pre- 

 molars are flattened for grinding. 



Fig. 220. Head of rhinoceros 

 American Museum of Natural History 



