594 UNGULATES. 



ridges of the upper molars are constant and characteristic of the 

 species, and materially aid in the determination of fossil remains. 



Even in existing species so nearly allied as the unicorn Rhino- 

 ceroses of India and Java, each might be determined by a single 

 detached molar tooth. The principal valley is bent back at its 

 termination in the Java species, but being shallower than the rest 

 of the valley, it is obhterated and the valley simplified in form 

 as in fig. 4. The posterior fold (e) is soon converted into an island ; 

 the chief fold is next insulated by the wearing down of the dentine 

 to its beginning, and is the last to disappear. 



The African Rhinoceros bicornis has a relatively larger molar, 

 especially in its antero-posterior extent ; the beginnings of the two 

 folds (ib. fig. 5, & & c), being deeper than their terminations, no 

 islands are formed in the progress of abrasion. In the Sumatran 

 Rhinoceros the valley (&) is relatively wider at its commencement, 

 and contracts to its termination, which is pointed, in little-worn 

 molars ; a simple secondary process projects from the posterior ridge 

 into the valley, and partially detaches the narrow and at first 

 triangular termination ; when attrition has reached the shallow 

 part of the valley at the end of the process, answering to / in fig. 5, 

 the entire termination of the valley is insulated : a second and 

 posterior island is formed when abrasion has removed the enamel 

 from the wide and shallow beginning of the posterior valley c. 

 Thus with regard to the first formed island c, which characterises 

 the abraded molars of the Indian one-horned and Sumatran two- 

 horned Rhinoceros, this results from the insulation of part of the 

 blind termination of the principal valley in the one-horned species, 

 and from the cutting off" of the whole termination of the valley 

 in the two-horned species. Cuvier, not having attended to this diff'e- 

 rence, failed to perceive that the fossil molar teeth which he 

 figures, loc. cit. PL VI, fig. 5, and PL XIII, fig. 4, and which 

 are copied in PL 138, figs. 6 k 7, belonged to two distinct species 

 of Rhinoceros. (1) Figure 6 is the second true upper molar tooth 



(1) He describes the tooth (PL 138, fig. 6) figured in his * Ossem, Foss. Rhinoceros,' PI. vi, 

 fig. 5, as follows : — " Fig. 5, est la cinquieme du cote gauche peu usee. On y voit aussi tres-bien 

 la fossette, resultant de I'union du crochet posterieur avec la colhne anterieure et I'echancrure 



