MAMMALS. 



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, in which the whole upper 

 surface of the body is covered with scales, arranged some- 

 what like those of a pine-cone. These scales, as already 

 mentioned (p. 98), are to be regarded as modified hair. 



ORDER II. RODESTTIA (The Gnawers). 



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

 rats and mice in this direction being shared by all mem- 

 bers of the order. They have no canine teetn ; the molars 



FIG. 43. Skull of rauskrat (enlarged), showing the gnawing incisors and absence 



of canines. 



are usually f, 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 through- 

 out life. As fast as they wear away they are renewed from 

 below. In each incisor two parts can be distinguished: 

 the anterior face of the tooth is covered with a very hard 

 layer (enamel), while the posterior surface is composed of 

 a much softer dentine. This dentine wears away much 



