1394 CLASS MAMMALIA. 



jaws obtained by Drs Kaup and Klipstein from the Lower Pliocene 

 of Eppelsheim, in Hessen-Darmstadt. Dinotherium was an animal 

 of the bulk of an Elephant, characterised by the presence of a pair 

 of tusk-like, backwardly-curved incisors in the lower jaw, and by 

 having in the adult five cheek-teeth, of which the two first are pre- 

 molars. The true molars carry simple, low, transverse ridges ; of 

 which there are three in the first tooth of the series (fig. 1266, a, b), 

 and two in each of the others. The upper premolars differ from 

 the true molars in having their two transverse ridges connected on 

 the outer side by a longitudinal ridge, which causes these teeth to 

 be of the lophodont type of those of the Tapirs. In the young 

 animal there were three milk-molars in each jaw, which resemble 

 the true molars in structure ; each of the first two having a pair of 

 transverse ridges, while the third has three of these ridges, and thus 

 resembles the first true molar. The number of ridges in the 

 milk and true molars may therefore be represented by the ciphers 



2.2.3 3.2.2 

 Mm. , M. : the import of which we shall notice 



2.2.3 3 • 2 • 2 



under the head of the Elephantida. Dinotherium indicum, from 

 the Upper Miocene and the Lower Pliocene of North-western 

 India, was probably nearly allied to the European species. 



Family Elephantid^. — With this family we enter a group of 

 animals in which the succession of the cheek-teeth presents such 

 marked peculiarities as to require special notice at the outset. In 

 the existing members there are normally six of such teeth, which 

 increase gradually in size and complexity from the first to the last. 

 The last three of these teeth correspond to the true molars of less 

 aberrant Ungulates, while the anterior ones represent the last three 

 milk-molars of the same. These milk-teeth are not succeeded by 

 premolars, but the whole series of teeth is gradually pushed forwards 

 in the jaw ; the anterior teeth being worn away and their roots 

 absorbed before the hinder ones come into use. In consequence 

 of this arrangement, and the large absolute size of the teeth, there 

 are never more than portions of two cheek-teeth on either side of 

 each jaw in use at any one time, as is shown in fig. 1264. The 

 cheek-teeth of the existing Elephants will therefore correspond to 

 Mm. 2 + Mm. 3 + Mm. 4 + M. 1 + M. 2 + M. 3 of the typical series, 

 but it is not improbable that in very rare instances Mm. 1 may also 

 be developed. If we had to depend entirely on the evidence of the 

 existing forms, there might be some doubt as to the serial homology 

 of the three teeth which we reckon as milk-molars ; but this question 

 is set at rest by some of the fossil forms, in which these teeth were 

 vertically succeeded by small, and usually functionless, premolars. 

 The total disappearance of the premolars, and the persistence of 

 the milk-molars in the higher forms, is the widest departure from 



