FAMILY CASTORHXE; BEAVER. 261 



ice closes their holes, they attack and devour one another. 

 Their fur, like that of the Beaver, is peculiarly adapted for 

 felting ; and from four to five hundred thousand skins are 

 annually imported into England, for the manufacture of hats. 



229. The preceding group is probably to be associated, with 

 the Beaver, in the family CASTORID^E; of which the Beaver is to be 



FIG. 132. BEAVER. 



regarded as the type. This animal is distinguished from all 

 other Rodents, by its horizontally-flattened tail, which is of a 

 nearly oval form, and covered with scales ; the hind feet are 

 webbed, and, together with the tail, serve to propel it through 

 the water with considerable facility. The incisor teeth are 

 very large and peculiarly hard ; and they were employed by the 



North American Indians, as instru- 

 ments to cut bone and to fashion 

 their horn-tipped spears, till they were- 

 superseded by the introduction of 

 iron tools from Europe. The molar 



FIG. 133. MOLAR TEETH OF THE 



BEAVER. teeth are four, above and below, on 



each side ; they are furnished with 



layers of cortical substance, as well as with ivory and enamel 

 (ANIM. PHYSIOL., 178) ; their crowns are flattened ; and they 

 present very much the aspect of a riband folded upon itself, aa 



