TEETH OF UNGULATA. 359 



having a disproportionate antero-posterior extent, and supporting 

 three transverse eminences, with an anterior, posterior, and inter- 

 nal basal ridge. The Dinothere resumes the tapiroid character, 

 and differs from the Mastodon, inasmuch as the posterior molars, 

 m 2 and 3, instead of having an increased antero-posterior extent 

 and more complex crowns, increase only in thickness, and support 

 two instead of three transverse eminences ; they have also an an- 

 terior and a posterior basal ridge. In the lower jaw the first 

 premolar, p 3, is implanted, like that above, by two fangs ; but it 

 has a smaller and simpler crown, which is narrower in proportion to 

 its antero-posterior extent, and is almost entirely occupied by the 

 antero-posterior ridge, only the posterior of the two inner tuber- 

 cles being developed ; thus the crown presents more of a trenchant 

 than of a grinding character ; the second premolar, p 4, supports 

 two transverse ridges. The third of the permanent series, which 

 is the first true molar, m l, has three transverse ridges, like the 

 one above, but is relatively narrower; the second, m 2, and third, 

 m 3, true molars have each large square crowns, with two trans- 

 verse ridges, and an anterior and posterior talon, the latter being 

 more developed than in the corresponding molars of the upper 

 jaw. 



The generic peculiarity of the Dinotherium is most strongly 

 manifested in its tusks. These, fig. 288, i, are two in number, 

 implanted in the prolonged and deflected symphysis of the lower 

 jaw, in close contiguity with each other, and having their exserted 

 crown directed downward and bent backward, gradually de- 

 creasing to the pointed extremity. In jaws with molar teeth of 

 equal size, the symphysis and its tusks offer two sizes ; the larger 

 ones, which have been found four feet in length, with tusks of 

 two feet, may be attributed to the male Dinothere ; the smaller 

 specimens, with tusks of half size, to the female. The ivory of 

 these tusks presents the fine concentric structure of those of the 

 Hippopotamus, not the decussating curvilinear character which 

 characterises the ivory of the Elephant and Mastodon. No cor- 

 responding tusks, nor the germs of such, have yet been discovered 

 in the upper jaw of the Dinotherium. 



D. Proboscidia. — The dentition of the genus Elephas, the sole 

 existing modification of the once numerous and varied Probosci- 

 dian family, includes two long tusks, fig. 289, one, i, in each of the 

 premaxillary bones, and large and complex molars, ib., d 4, m i, 

 m 2, in both jaws: of the latter there is never more than one 

 wholly, or two partially, in place and use on each side at any 

 given time, the series being continually in progress of formation 



