358 A MANUAL OF DENTAL ANATOMY. 



elephant, was widely distributed over the world. The dental 

 formula is not quite the same for all the genus, for in some 

 no premolars existed. 



102 33 



i. _ c. - prm. - milk molars _ m. r 



The upper incisors formed nearly straight tusks, seven or 

 eight feet in length ; the lower incisors also grew out hori- 

 zontally from the front of the jaw, but in some species the 

 lower tusks are rudimentary, are lost early, or "are altogether 

 absent, thus more nearly approaching to the condition met 

 with in the elephant. 



The several molar teeth of the Mastodon increased in 

 size from before backwards. The crowns were built up of 

 deep and strongly pronounced transverse ridges, of which 

 the last molar had the largest number. The apices of the 

 ridges, before being at all worn, were divided up into several 

 blunt nipple-like (mastoid) processes, upon which the 

 enamel was thick and dense, but the cement was thin, so 

 that the interspaces of the processes were not filled up level 

 by the latter tissue, as in the elephant. 



Very definite roots were formed to the molars, the wear- 

 ing down of the teeth being met by the worn teeth being 

 shed off altogether from the front of the series, whilst new 

 teeth were added to the back. Thus, just as in the elephant, 

 the whole number of teeth were not in place at one time. 

 ISTot more than three were in use at one time, and by the 

 time the last and largest molar was cut, there was but one 

 tooth remaining in front of it, and even this was soon lost, 

 the dentition thus being reduced to a single molar on 

 each side. 



As the succession of the molars in the Mastodon affords 

 a clue to the nature of the grinders of the elephant, it is 

 necessary to add a few words about it. Some Mastodons 

 had three milk molars, of which the last two were vertically 

 displaced by premolars, just as in most other mammals, 



