374 SYSTEMATIC ZOOLOGY. 



receives interest from the fact that it was first described 

 by Thomas Jefferson. 



The ant-eaters are true edentates in that they are 

 wholly without teeth. As their name implies, ants form 

 the chief part of their food; their claws are well adapted 

 for digging into the nests, the tongue is very long and 

 extensible, while the salivary glands pour out a thick, 

 sticky secretion which fastens the ants to the tongue. 

 The true ant-eaters are natives of South America, but in 

 Africa and India are allied forms with teeth, which also 

 feed upon ants. Among these are the pangolins (fig. 163) 

 in which the whole upper surface of the body is covered 

 with scales, arranged somewhat like those of a pine-cone. 

 These scales, as already mentioned (p. 364), are to be 

 regarded as modified hair. 



ORDER III. RODENTIA (The Gnawers). 



The rodents are the gnawers, the well-known abilities of 

 rats, mice, and beavers in this direction being shared by 

 all members of the order. They have no canine teeth; 



FIG. 164. Skull of muskrat (enlarged), showing the gnawing incisors and 



absence of canines. 



the molars are usually |, while the incisors vary between 

 f, |, and f . These incisors demand a moment's attention. 

 These teeth have persistent pulps, i.e., they continue to 

 grow throughout life. As fast as they wear away they 



