64 CLASS MAMMALIA. 



They have five toes on every foot ; the hinder ones 

 are united by membranes, and there is a double and 

 oblique claw on that one which follows the thumb ; 

 their cheek-teeth, four in number, and with flat co- 

 ronals, are so formed as to show one sloping edge 

 at their internal extremity, and three at their exter- 

 nal in the upper row, and exactly the reverse in the 

 lower. 



The Castors are tolerably large animals, and their 

 life is altogether aquatic. They use equally their 

 feet and tail in swimming. As they live principally 

 on the bark of trees and other hard substances, their 

 incisors are very powerful, and shoot up vigorously 

 from the root in proportion as they become worn 

 in front. They also make use of these teeth in cut- 

 ting trees of every kind. 



Large glandulous pouches which border on the 

 prepuce, produce a pommade of a powerful odour, 

 used in medicine under the name of castoreum. In 

 the two sexes, the organs of generation border on 

 the extremity of the rectum, so that there is but a 

 single external aperture. 



The Castor of Canada (Castor Fiber), Buff. VII. xxxvi. 



Is larger than the Badger. Of all quadrupeds it 

 exhibits most industry in the fabrication of its 

 dwelling. These animals associate together for this 

 work in the most solitary parts of North America. 



The Beavers generally choose the deepest waters, 

 which are not likely to be frozen to the bottom, and 



