11)6 Mr. U. I. Pocock on a Case of 



XVIII. — A Case of Abnormal Dentition in a Dhole, or Indian 

 Red Dog (Cuon dukhunensis). By R. I. Pocock, F.L.S., 

 F.Z.S., Superintendent of the Zoological Society's 

 Gardens. 



When discussing variation in the premolars of the Canida?, 

 Mr. Bateson * commented on the rarity of the occurrence of 

 a fifth premolar in the lower jaw, only three or four cases 

 being known to him. Two of these were quoted by Hensel |, 

 the skulls presenting the abnormality being those of wolves 

 showing two teeth between the canine and the second 

 premolar, one in the right mandible and the other in the left. 

 The other cases were those of domestic d )gs, one presenting 

 five premolars on both sides of the lower jaw, the other 

 showing two alveoli where the first premolar should have 

 been. 



Since the number of recorded instances is so small, it is of 

 interest, I think, to report the presence of a supernumerary 

 premolar in the right mandible of a specimen of an Indian 

 dhole ( Cuon dukhunensis) that formerly lived in the Zoolo- 

 gical Gardens. 



The dentition of the left mandible is normal and resembles 

 that of the mandibles of two other specimens imported at the 

 same time, except that the posterior cusp on pm 3 is practically 

 absent and the roots of pm 2 are united. In the right mandible 

 also the cusp is absent and the roots of pm 2 are united. On 

 both sides pm 1 is single-rooted ; pm 2 , as stated, has two large 

 coalesced roots set in a correspondingly large constricted 

 alveolus; pm 3 has two large somewhat A -shaped roots. 

 There is no difficulty in homologizing these three teeth on 

 the two sides, their size and the shapes of the crowns and 

 roots making their identity unmistakable. The supernumerary 

 tooth lies between pm 2 and pm 3 and is not structurally quite 

 identical with either. Its crown is shorter than that of pm 2 , 

 and it has its posterior portion more widely rounded than is 

 that of pm 2 or of pm 3 . Like pm 3 it has two distinct roots, 

 but these are gradually attenuated and separated by a much 

 narrower cleft. 



On the left mandible with normal dentition the longitu- 

 dinal axes of the crowns of pm 2 and pm 3 lie in the same line 

 as the axis of the jawbone; and these teeth are separated 

 from the adjacent teeth, pm 1 and p>u\ and from each other by 



* ' Materials for the Study of Variation,' p. 211 (1894). 



f Morph. Jahrb. v. p. 046 (1870) ; also Bateson, p. 213. no, 231. 



