1880.] DENTAL CHARACTERS OF THE CANID.E. 283 



number andthe kinds of teeth which existed in the earliest ancestors 



ot the Canidae and that the lobate mandible is similarly inherited 



rom them, it becomes necessary to seek, for the primitive forms of 



the Carmvora which probably stood in the same relation to Amnhi. 



cyo« as Otocyon does to Canis and Vulpes, in still older formations. 



Wothmg IS at present known of the Mammals of the Cretaceous 



epoch ; and from the older Eocene the only forms which bear upon 



the present question are Arctocyon, Pterodon, and Hycenodon. Of 



the farst too httle is known to warrant speculation. With resoect 



the two latter, M. Filhol's observation! have conclusively nro^ved 



(hat they have as httle to do with the Didelphia in dentition as in 



other respects ; and he has described an interesting form, Oynh,^. 



melon, the upper dentition of which approaches that of Pterodoi whde 



Its mandibular teeth present resemblances to those of Gynodktis 



1 do not suppose, however, that Pterodon (and still It^UlycEnodon^ 

 hes in the direct line of ancestry of the Canida.. On the contrty 

 they appear to constitute a peculiar branch of the stock of the Car 



'^'^^:^^^:^^ '^ ''' ^"^^^^^-- *^^- -e possessed 

 In fact, in Cenfefes the molar teeth of both jaws increase in size 



U at those of all the Carnivora may be readily derived from them 

 The trihedral pnsm which constitutes the chief part of the fir^t 

 upper molar of Oentetes obviously answers to the triangular elevadon 

 on the crown of the corresponding tooth of 0^ey.«,"which tinj. 

 nates in the two outer and the two inner cusps; and the n^ hi 

 difference between the two is that the cingulum is lal-ger and extend 

 much nearer to the summits of the cusps in Olocyon than in CenllZ 

 In the mandibular teeth, again, the first molar of CenfeZte: 

 sents exactly the same number of cusps, disposed in the same^^- 

 as m that of Otocyon, the difference between the two lyin<. n eS 

 m the different proportions of the parts. The exact coiTesp°onde, c« 

 n plan of these teeth is the more interesting, since, in Cen I testis 

 easy to trace the progressive changes by whidi the simple and pri „ 

 tive character of the Mammalian cheek-tooth exhibited by thi most 



^;:::s^''''' '-'^ '"^^ ^^'^p^- ^^--^-^ «^ ^^- --ns^of 



This is particularly obvious in the lower cheek-teeth, in which 

 the crown of the most anterior premolar is simply tricuspda^e w t 

 the anterior andthe posterior cusps very small and the apex of the 

 principal cusp simple. In the next premolar the prindpal cu n 

 appears clef near its apex, in consequence of the development of 'a 

 small secondary cusp on its inner side ; the anterior cusp s ll er 

 and the posterior both higher and thicker. In the third pra^iolar 

 and ,n the molars, the anterior cusp is still higher; theK Sv 

 cusp IS as large as that from which it is derived,°so that it answ r^ J 

 Oie anterior internal cusp, while the former principal cusp akes he 

 pla e of the anterior external cusp of the typical canine to^oth The 

 posterior cusp, become very broad, and divided by a faint median 

 depression, represents the posterior external and posterior iSerna] 



