210 FAUNA AMERICAN-A. 



dense structure, composed of concentric laminse., 

 which vary from two to four-tenths of an inch in 

 thickness, and do not display those curv^ilinear 

 lozenges so conspicuous in the tusk of the Ele- 

 phant. 



Note. This difference of structure noticed in the 

 tusks of the Mastodon and Elephant, first observed 

 by Cuvier, is overlooked by Desmarest, who attri- 

 butes to each a similarity of structure; the fact, as 

 above stated, we have repeatedly verified by ob- 

 servation. 



Molars rectangular, formed simply of an osseous 

 substance, surrounded with enamel, without ce- 

 ment or cortical matter, having their crowns ele- 

 vated into large points, disposed in pairs, varying 

 in number, according to the age and position of the 

 tooth, from six to ten ; these molars advance in 

 the jaws in proportion as they become developed; 

 their crowns displaying, when half worn, as many 

 lozenges of enamel as there were originally points 

 to the tooth; very old animals have only one mo- 

 lar on either side of each jaw. 



The Os incisiviim is prolonged and pierced with 

 large alveoles for the tusks. 



Inferior jaw terminated before by a point, in 

 which is a canal. 



Neck very short; extremities very long, and 

 terminated by five toes; tail moderately long; 

 seventeen pairs of ribs, of which six are true. 



