THE TEETH OF PROBOSCIDEA. 359 



but the first milk molar was not so replaced (Mastodon 

 angustidens). There appear to have been Mastodons in 

 which no vertical succession at all took place, i.e., in which 

 there were no premolars, and others in which there was 

 but one. 



No doubt can be entertained as to the homologies of the 

 teeth, even in those Mastodons which are not known to 

 have any vertical succession, because analogy with those 

 other species in which the second and third molars, counted 

 from the front, were vertically displaced by nearly func- 

 tionless premolars, tells us that the three front molars are 

 milk molars. Now elephants develop six molar teeth on 

 each side ; the elephant is in the same case, quoad its molars, 

 as the Mastodon Ohioticus, which had no vertical succes- 

 sion, so that we thus know the elephant's grinders to be 



,33 

 dm.-m._ 



Dr. Falconer mentions an elephant from the Sewalik Hills 

 (E. planifrons) in which two rudimentary pre-molars, of no 

 functional importance, actually existed, and so the deter- 

 mination of the elephant's working teeth as 



, 3 3 



dm. - m. - 



3 3 



rests not only upon analogy, but upon actual observation. 



The Dinotherium, a large animal, not unlike the Sirenia 

 in the character of its cranium, which was probably of 

 aquatic habits, was remarkable for possessing large tusks, by 

 analogy known to be incisors, in its lower jaw, none being 

 present in the upper jaw. The tusks projected downwards 

 at right angles with the body of the jaw, and were curved 

 backwards. The portion of jaw about the symphysis was 

 deflected downwards, so as to afford an adequate implanta- 

 tion for these anomalous tusks. 



