68 THE AMERICAN BEAVER. 



the pulp organ is atrophied; the tooth is smaller within 

 than without the socket. In a sec- 

 ^^* ■ tion of the tooth the tips of the enamel 



inflections are seen of different lengths, 

 as they have become gradually closed. 

 Corresponding changes have taken place 

 in the sockets; their bulbous projec- 

 tions in the upper jaw being no longer 

 visible. While, therefore, the molars 



Section of "root- /» -i i ^ ii L^ i 



ed" molar ^^ ^'^^ beavcr are both rootless and 

 rooted at different stages in the growth 

 of the animal, the latter is the characteristic of its 

 mature condition. 



MUSCLES. 



It would exceed our limits to enumerate the mus- 

 cles of the beaver. Their specification is the less ne- 

 cessary as the muscles of the mammalia present few 

 important variations from the human standard.. They 

 may, however, be so modified in connection with par- 

 ticular functions as to merit notice, and for this rea- 

 son we shall allude briefly to the muscles of mastica- 

 tion. The power required for cutting and grinding 

 hard ligneous substances is supplied in the beaver by 

 the development of the masseter muscle. This mus- 

 cle arises from the whole length of the lower part of 

 the malar bone, and is inserted into the crest of the 

 lower jaw, and side of the jaw to the anterior end 

 of the crest. It is strengthened by tendinous fibres 

 passing from the root of the crest into the body of the 

 muscle. At the junction of the superior maxillary 

 and malar inferiorly a tendon runs forward to the 

 process covering the ante-orbital foramen. The inner 



