RHINOCEROS HEMITCECHUS. 333 



them separately. A very advanced stage of abrasion is pre- 

 sented by the antepenultimate or m. 1 of fig. 2 of PI. XVI. 

 The posterior valley is reduced to a small pit, and the large 

 sinuous transverse valley to a diagonal fossette, from the pos- 

 terior wall of which every trace of a crochet or of a combing 

 process has disappeared. The penultimate (m. 2) of the same 

 figure, although less worn, has lost the greater part of the 

 mass of the crochet by the waste of abrasion, and the middle 

 valley, in consequence, forms a fissure of nearly uniform width, 

 much reduced in expansion at its extremity. 



Next, in regard to the last true molar. Of all the grinding 

 teeth in the genus Rhinoceros, the last true molar of the 

 upper jaw is that which presents the greatest difference of 

 form and the most pronounced characters for distinguishing 

 the species. Fortunately we possess, in the series of the 

 Gower specimens, a complete set of illustrations, showing 

 this tooth in every stage, from that of the intact germ up to 

 the worn crown of the aged animal ; and the modifications of 

 form which it presents are so peculiar, and of so much syste- 

 matic interest when considered in connection with the partial 

 bony septum, that I shall not hesitate to enter into more 

 detail in describing it than in the case of the penultimate and 

 antepenultimate. This is the more necessary, as De Christol, 

 the most original and weighty authority on the subject since 

 the time of Cuvier, has omitted the last molar in his elaborate 

 analysis, under the belief that it yielded no specific characters 

 of importance. 1 In order to make the description clear, it is 

 requisite to refer to the general composition of the crown of 

 a true molar in Rhinoceros, as indicated by Cuvier. Taking 

 the penultimate as the type, the crown is nearly rectangular 

 in outline and bounded by four sub-equal sides ; the outer 

 and inner, and the anterior and posterior, forming parallel 

 sides of the square. The outer side (a b of the teeth B and C 

 of fig. 1 PI. XLIII., 2 Cuvier's Oss, Fossiles (supports a longi- 

 tudinal ridge or colline, from either extremity of which a 

 transverse flexuous ridge is given off at a right angle, forming 

 (a c) an anterior colline, and (b e) a posterior colline, parallel 

 to each other, but separated by a sinuous transverse valley. 

 The terminations or barrels of these collines constitute the 

 inner side of the square. The anterior side forms a straight 

 unbroken line, and in all the species presents nearly the same 

 uniform character, except in the greater or less amount of 

 development of its basal bourrelet. The posterior side is the 

 most subject to modification. It is shorter than the anterior, 

 deeply notched by an antero-posterior fissure, generally 



1 De Christol, op. tit. p. 47- 



2 Corresponds to PI. v. of Rliin. in vol. ii. of 3rd cd. 1825.— [Ed.] 



