TEETH AND THEIR VARIATIONS. 



209 



into one with a selenodont form, although of a low- 

 crowned type; and we may infer from this that the 

 owners of the latter type of teeth tended to depart 

 more and more completely from the mixed diet of the 

 Pigs towards the purely herbaceous diet of the Deer 

 and Cattle. So far, however, as we are acquainted 

 with these intermediate animals, their general type 

 of organisation appears to have been very like that 

 of the Pigs. We have now, however, to consider the 

 teeth of the modern Deer and Cattle, which we shall 

 find to be of a still more complex type. Fig. 69 shows 

 a somewhat worn cheek-tooth of one of the smaller 

 Deer, which will be seen to be but a 

 step in advance of the tooth represented 

 in Fig. 68, the outer crescents having 

 now become still more compressed and 

 flattened, and both these and the inner 

 ones having acquired a considerably 

 greater elevation, so that the bottom of 

 the valleys between the crescents is no 

 longer visible. In some other species of 

 Deer, as well as in many of the Antelopes, 

 the crescents of the teeth become very 







much taller (Fig. 70), so that the inter- 



veiling valleys form deep pockets, with 



narrow entrances, and the whole type of tooth is so 



utterly unlike that of the Pigs that, when the inter- 



mediate extinct types were unknown, it is small wonder 



that the older naturalists failed to recognise the intimate 



connection that really exists between the Pigs and the 



ttw 



" f aD f r - v . iewed 



from the grinding 



surface and from 



the outer side. 



