50 THE AMERICAN BEAVER. 



elles se separent aisement apres la mort de ranimal." 

 Thin longitudinal and transverse sections exhibit the 

 true character of this structure. The tail is com- 

 posed largely of a dense fatty tissue; upon this lies 

 the derm or skin, 07'" in thickness, its outer sur- 

 face being serrated, with the points of the serratures 

 toward the end of the tail. Over the serratures is ex- 

 tended the tough horny epiderm, gs" to ^V in thick- 

 ness, which is inflected under the serratures, so as to 

 present the imbricate appearance. The longitudinal 

 divisions are merely dips or depressions, not imbricate. 



Fig. 1. 



Longitudinal section of scaly tail, twice the natural size. 



The beaver, being an aquatic as well as a land ani- 

 mal, presents two types of structure. The arms and 

 hands are small, are adapted to burrowing, and, being 

 capable of partial supination, the hands may be used 

 for holding substances between them. The hind ex- 

 tremities are strongly developed, and are constructed 

 after the aquatic type. The feet have been compared 

 to those of the turtle. Each extremity has five digits. 

 The back of the hand is thickly covered with short 

 hairs; the palm is naked, with a tough black epi- 

 dermis, and two tubercles, one opposite the fifth fin- 

 ger, the other under the metacarpals of the second, 

 third, and fourth. The fingers are furnished with 

 long claws, of which that of the third finger is the 

 longest, 92'" long, and 20'" broad. The first finger 

 (thumb) is shorter than its claw. Next in length is 



