KHINOCEROS. . 91 



three premolars increase slightly to the last one, and they are quadrate and have 

 the inner side convex and narrowest. 



The outer side (4) of these teeth forms a large quadi-ilateral surface with rounded 

 angles. It is slightly convex, and is feebly waved longitudinally. At the fore part 

 a narrow fold descends from the base and expands towards the triturating margin ; 

 but it is successively less developed forward, and in the first of the series is rudi- 

 mentary. This fold increases in depth in the true molars, and is quite character- 

 istic of the outer part of these teeth in Rhinoceros, as it does not exist in Palaeo- 

 tJierium, Titanotherium , nor Ancliitlierium. 



In advance of the fold just described, the antero-external margin of the molars 

 projects forward and slightly outward, and looks like an independent column or 

 buttress, and is the shortest portion of the outer lobes. 



The triturating margin of the latter, in the specimens of premolars under especial 

 examination, is bilobed and acute. 



The inner surface of the postero-external lobe is a little convex, and from the 

 same surface of the antero-external lobe in the third and fourth premolars an abrupt 

 fold projects into the principal valley of the teeth (5). This fold, when the teeth 

 are partially worn away, gives the termination of the principal valley a bifurcated 

 appearance; and in Rhinoceros indicus and Rhinoceros tichorinus it is the extension 

 and confluence of the fold with the anterior part of the postero-internal lobe of the 

 teeth which produces a division of the principal valley, represented when the teeth 

 are considerably worn away by two enamel pits. 



The internal lobes have acute summits and more or less expanding bases, and, 

 except in the first tooth, their inner extremities for more than half their depth are 

 confluent, so that the principal valley is a deep pit, with shelving sides and an 

 internal notch (5, 6) . 



In the fourth premolar, the postero-internal lobe is a sigmoid fold projecting from 

 the confluence of the outer lobes. 



In the three premolars in advance, the postero-internal lobe consists of two 

 portions; an inner pyramid with two broad sides directed obliquely antero-poste- 

 riorly, and a bent fold extended between the confluence of the outer lobes and the 

 outer side of the pyramid, and separating the two characteristic valleys of the 

 teeth. This fold does not reach the summit of the inner pyramid, nor of the outer 

 lobes, and it looks more like a narrow partition separating the valleys than a 

 constituent portion of the postero-internal lobes. 



The antero-internal lobe of the premolars, except in the first, is directed trans- 

 versely inward on a line with the characteristic fold of the outer surface of the 

 teeth, and it expands as it approaches its termination, and antero-internally swells 

 into a sort of couoidal buttress, gradually increasing in distinctness from the second 

 to the last premolar. In the first premolar it appears only as a small, compressed 

 mammillary eminence of the basal cingulum. 



The latter, as in Rhinoceros occidentalis, is well developed upon all the premolars. 

 In the specimens under special examination, ossification had not yet advanced to 

 its production, externally (4), but in older specimens in this position it measures 

 over a line in depth (1). At the postero-external margin of the teeth it very 



