44 THE MAMMALIA. 



defeat, even though, in most cases, this takes place 

 with the utmost slowness. Instances of the loss of 

 milk teeth are met with among the Marsupials and 

 seals. The whole phenomenon belongs to the 

 chapter of ' abbreviated development.' It was our 

 intention here merely to point out this view of the 

 subject, in order to make use, in what follows, 

 of the designations given to different parts of the 

 jaw, according to position and time, since Cuvier's 

 and Owen's classical investigations. 1 



Let me here repeat that the specialisation of 

 the dentition frequently runs parallel with a speciali- 

 sation of the limbs. Thus, in comparison with its 

 geological ancestors, the dentition of the horse is 

 very specialised, and this is equally evident as 

 regards its foot, the transformation of which, from 

 a five-toed member not specially suited either for 

 running, grasping, or climbing into a one-hoofed 

 member, so admirably adapted for running, has 



1 Example. In man the milk teeth, the denies decidui, con- 

 sist of the cutting teeth (incisors), the canine or eye teeth, and 

 the two front cheek-teeth. In addition to these there are the 

 three back cheek-teeth that have no predecessors. The teeth of the 

 full-grown man are indicated thus : i | c \p \ m f , i.e. on either 

 side above and below two incisors, one canine, two premolars 

 and three molars. Although Cuvier of course knew the dents 

 de lait and the dents de remplacement, still Owen was the first 

 rigorously to carry out the designation. 



