414 GENERAL ZOOLOGY 



third digit is used for support. The elephants have five toes, 

 each incased in a short nail. The two living species of ele- 

 phants would undoubtedly be removed to a separate order if 



fossil forms had not been 

 discovered 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 pres- 

 FIG. 219. Skull of Peccary, showing teeth ^ __ incisors> can i nes , 



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. 

 cam's, a dog), fill the space between the incisors and premolars. 

 The canines are often elongated to form tusks for defense or 

 for obtaining food (see Fig. 219) ; the incisors serve to crop 

 the herbage ; the molars and premolars are flattened for 

 grinding. 



Horns for defense have been developed in many species 

 of ungulates. They are of various sorts. The rhinoceroses 

 (Fig. 220) have one or more median horns, which are com- 

 posed of a thickened and hardened portion of the skin and 

 hair, covering a short protuberance of the skull. In the 

 giraffes there are one or two pairs of horns consisting of a 

 layer of skin over bony processes of the skull. Neither in 

 the rhinoceros nor the giraffe are the horns ever shed. In the 

 North American pronghorn antelope (Antiloca'pra america'na) 

 the horns are branched and consist of a hardened and thick- 

 ened skin on a bony core. The thickened skin is shed peri- 

 odically but the core is retained. The horns in true antelopes 



