RHINOCEROS. 85 



The bottom of the single, simple valley of the last molar is nearly level its 

 whole length, and is bounded at its entrance by a prominent portion of the basal 

 cingulura. 



The principal valleys of the sixth and fifth molars are successively shallower 

 externally, and deepen in a sloping manner toward their entrance, where they are 

 partially closed by a prominent portion of the basal ridge, and hence, in the tritu- 

 ration to which the teeth are subjected, these valleys are obliterated from without 

 inward, and leave no isolated enamel islands, or pits, as in the molars in advance, 

 or in the corresponding teeth of Rhinoceros indicus. 



In the sixth molar, the posterior valley is as deep externally as the principal 

 valley, and in the fifth molar it is deeper. 



In the specimen under consideration, trituration has left the principal valley of 

 the fifth molar as a tract of enamel, which is narrow and slightly depressed ex- 

 ternally and curves backward and inward, and expands and deepens as it approaches 

 its termination. 



In the second to the fourth molar inclusive, the inner lobes at their bases in- 

 ternally are confluent, and from the degree of trituration which the third and fourth 

 molars have undergone in the specimen, the principal valleys are left as simple, 

 oblique, trilateral pits or islets of enamel, occupying the centre of the exposed 

 dentinal surface. In the second molar, from the less degree of confluence of the 

 inner lobes internally, in addition to its being less worn, the principal valley still 

 remains open. 



In the fourth molar, the postero-internal lobe is not much more than half the 

 thickness of that in advance ; but in the second and third molars, the inner lobes 

 are nearly equal in size. 



The basal cingulum of the molars, from the second to the fourth inclusive, en- 

 velops the base of the postero-internal lobes to a much greater extent than upon 

 the antero-internal lobes, or rather these are shorter than the former, and the basal 

 ridge descends in its course postero-internally, where it is very thick and strong, 

 and is so prominent, that when the teeth are worn down so that the principal val- 

 leys remain only at their outer extremity as very small pits, the posterior valleys, 

 which are very nearly as deep, would be left in the same condition. 



The first molar in the specimen presents an almost equi-trilateral surface of ex- 

 posed dentine, with the internal lobes of the crown curving inward and backward 

 and dilating at their termination, and with the antero-external lobe forming its 

 anterior rounded and prominent apex. Portions of a basal ridge connect the 

 bases of the inner and the antero-external lobes together. The short principal 

 valley remains as a narrow tract of enamel constricted at the middle and deepened 

 at both extremities. The posterior valley remains as a small trilateral islet of 

 enamel. Between the antero-external and internal lobes the basal ridge forms a 

 broad cul-de-sac. 



Inferior Molars.— {^\. XIII. 2-6.) The teeth, preserved in the fragments of lower 



jaws referred to, belong all to the posterior four molars, and these do not differ in 



their form from those corresponding to them in recent species of Rhinoceros. A 



basal ridge with a rough margin exists in all, but is obsolete on the inner side of the 



12 • 



