135 



ovate, 1.1 inches long and f of an inch high ; the posterior side 

 being the smaller. The aperture near the anterior extremity of 

 the jaw, has a subquadrangular form, a little more than half an 

 inch long, and a little less than half an inch in height. 



The portion of the left branch of the jaw remaining, extends 

 back to the origin of the first tooth, exhibiting the broad, smooth 

 channel, or groove, occupied by the tongue. The abrupt deflec- 

 tion of this groove anteriorly, and the want of a beak, or prolong- 

 ation of the bone in front, excludes this fragment from the Mas- 

 todon longirostris ; and the proportionate breadth of the teeth, as 

 clearly indicates that it does not belong to the Mastodon angusti- 

 dens. I therefore conclude that the specimen belongs to the 

 M. giganteus. 



On referring to works on the Mastodon giganteus, I find it 

 stated, that there are six molar teeth in each branch of the jaws. 

 These teeth are produced at different times, those in front being 

 shed, while others are forming behind. Of these teeth the 

 Jlfth * corresponds with the first, in the specimen before me. 

 This indicates an animal of considerable age, having already 

 shed four teeth on each side of each jaw, or sixteen teeth in all. 

 The middle tooth in the specimen, corresponds with that of the 

 sixth and last, as described by Dr. Warren, so that the posterior 

 tooth is one not before observed in any of the bones heretofore 

 found. 



If we admit that the teeth advance as the animal increases in 

 age, those in front being shed, while others are formed in the 

 posterior portion of the jaw, I see no good reason why this pro- 

 cess may not be continued indefinitely, and the ultimate number 

 of teeth be regulated by the age and healthful condition of the 

 individual. In this view of the subject, there are no permanent 

 molars. Disease or death may arrest the process of dentition, at 

 any stage of its progression ; and there may be instances, where 

 the last formed tooth is considerably advanced, without the form- 

 ation of others behind. Such animals would soon become tooth- 

 less. Other individuals, of more vigorous growth, may be sup- 



* As described in " The Mastodon giganteus of North America," by John C. 

 Warren, M. D. Boston, 1852. p. 68. I am indebted to the liberality of the au- 

 thor, for a copy of this^superb and truly excellent work. 



