1880.] E. Lydeklcer— iVb^PS on the Dentition of Rhinoceros. 141 



B. smiatrensis, there is in the adult state no median pair of lower 

 incisors,* and it is, therefore, probable that permanent middle lower 

 incisors are never developed in this species. f 



In the living African species of Mliinoeeros, in the extinct Indian 

 a. deccanensis, and other extinct species, no permanent incisors, in either jaw, 

 were ever developed, and in the adult the symphysis of the mandible and 

 the premaxillse are consequently edentulous. It has been said that three 

 pair of lower incisors were developed in S,. sivalensis, but none of the 

 lower jaws of the genus figured in the ' Fauna Ant. Siv.' show more than 

 two pairs of these teeth, and none are present in the specimen referred to 

 a. sivalensis. 



From the foregoing brief notes it will be gathered that the dental 

 system of the genus Rhinoceros presents very considerable differences in 

 different species, and occasionally in different individuals of the same 

 species. These differences are mainly due to the varying extent to which 

 specialization has operated in the genus, and to the occasional develop- 

 ment by ' reversion' of teeth normally absent. 



The genus Rhinoceros (using the term in its original comprehensive 

 sense) is indeed one of those in which the dental system may be said to be 

 in a condition of change, and this variability in the matter of the develop- 

 ment or suppresion of certain teeth in species and individuals, appears to me 

 to render the splitting up of the old genus into a number of new genera 

 or subgenera (except in the case of Acerotherium) a very questionable 

 measure. The relative prominence or insignificance of the anterior teeth 

 may be traced in a graduated scale from one species to another as has been 

 most ably done by M. Gaudry in his invaluable work already quoted in 

 this ^aper. 



Explanation op Plate YIL 



Fig. 1. The left upper dentition of an immature specimen of R. indicus, showing 

 the germs of two permanent incisors {i}, «'.-), four milk-molars {m.ni^, m.m?, m.m.\ 

 m.m.'*), first and second true molars {m.^, >«."), and the alveolus of the third (w.^). 

 (The animal to which this skull belonged was killed hy Mr. W. T. Blanford.) 



Fig. 2. The left upper dentition of a somewhat older individual of the same spe- 

 cies, showing the alveolus of the first permanent incisor («'.'), the first and second pre- 

 molars {p. in}, p.m."), the third and fourth milk-molars (m.m:^, m.m.*), the first and 

 second true molars ()«.\ w.'*), and the alveohis of the thii-d (/«.•*), 



Both specimens are di-awn one half the natural size. 



* Professor Cope (loc. cit. p. 229) is in error when he gives two paii-s of mandi- 

 bular teeth to this species. 



t I should doubt if the lower jaw drawn in fig. 15 of plate 138 of Owen's 

 ' Odontography' as of R. stmatrensis belongs to that species. 



