140 E. Lydekker — Notes on the Dentition o/E!)inoeeros. [No. 3, 



We may, therefore, say that in JR. incUcus there are always developed in 

 the symjiliysis of the mandible two pairs of milk-teeth, and always one, and 

 occasionally two pairs of permanent teeth. When the middle pair of 

 milk-teeth are not replaced, they remain during the permanent dentition, 

 as in the analogous case of the first upper milk-molar. 



It now remains to consider the serial position of the teeth in question. 

 With regard to the middle pair of teeth, there can be no question but that 

 they are incisors, and probably the first of that series. With regard to 

 the homology of the larger outer pair of teeth, two views are entertained. 

 By the older writers, this pair of teeth were unhesitatingly classed as 

 incisors ; a view adopted both by Prof. Huxley and by Prof. Owen. Lat- 

 terly, however, some writers, among whom may be mentioned Professors 

 Cope* and Gaudry,t have come to the conclusion that this outer pair of teeth 

 are really canines, apparently from their resemblance to the undoubted 

 canines of certain genera of extinct Mammals. To distinguish between a 

 canine and an incisor tooth in the lower jaws of animals in which the 

 incisors are reduced and^no upper canine is present, is indeed a matter of 

 extreme difiiculty, and I do not desire on the present occasion to enter into 

 the reasons either for or against the innovation. I provisionally, however, 

 adopt the old nomenclature. J With this view of the homology of the 

 teeth in question, the anterior milk dentition of B. indicus may be formu- 

 lated as follows: — c. ll^ ^. ^> the adult dentition will be normally c. — 



0—0 3—2 0-0 

 ™ 0-0 .1-1 , n 0—0 . 2—2 



m.i. —t,—, or abnormally c. — i. — . 



In treating of the milk dentition of Wiinoceros, Professor Huxley§ 

 remarks of the two pairs of lower incisors that " it seems probable that 

 only one pair, in any case, are permanent teeth." I have shown that 

 occasionally in R. indicus both pairs may be replaced by permanent teeth, 

 and I now proceed to show that such is at all events sometimes the case in 

 another species. In a lower jaw of R. javanicus figured by De Blainville,|| 

 there are the germs of two incisors on each side in alveolo, below protruded 

 incisors ; the former, therefore, are clearly permanent teeth. I have no 

 means of knowing whether this replacement is abnormal or normal. In 



* Loc. cit. 



t ' Les Enchainements du Monde Animal : Mammiferes Tertiaries,' p. 50, et seq. 



X I may perhaps observe that there seems te he some discrepancy in M. Gaudry'a 

 nomenclature, since on page 68 of his work quoted ahove, he speaks of there being two 

 pairs of small incisors in the lower jaw of R. bicornis fafricanus), and yet does not pro- 

 duce any evidence to show that these teeth are not the homologues of the two pair of 

 teeth in the mandible of R. indicus, which are reckoned as incisors and canines. 



$ Loc. cit. p. 362. 



II ' Osteographie,' Atlas, Ehinoceros, pi. viii. 



