KINETOGENESIS. 343 



the latter to the dental series in modern Carnivora. 

 Why, for instance, were not the last molars modified 

 into sectorial teeth in these animals, as in the extinct 

 Hyaenodon, and various Creodonta. The answer ob- 

 viously is to be found in the development of the pre- 

 hensile character of the canine teeth. It is probable 

 that the gape of the mouth in the Hyaenodons was 

 very wide, since the masseter was situated relatively 

 far posteriorly. In such an animal the anterior parts 

 of the jaws with the canines had little prehensile power, 

 as their form and anterior direction also indicates. 

 They doubtless snapped rather than lacerated their 

 enemies. The same habit is seen in the existing dogs, 

 whose long jaws do not permit the lacerating power 

 of the canines of the Felidae, though more effective in 

 this respect than those of the Hyaenodons. The use- 

 fulness of a lever of the third kind depends on the ap- 

 proximation of the power to the weight ; that is, in the 

 present case, the more anterior the position of the 

 masseter muscle, the more effective the canine teeth. 

 Hence it appears that the relation of this muscle to 

 the inferior dental series depended originally on the 

 use of the canines as prehensile and lacerating organs, 

 and that its relative insertion has advanced from be- 

 hind forwards in the history of carnivorous types. 

 Thus it is that the only accessible molars, the fourth 

 above and the fifth below, have become specialised as 

 sectorials, while the fifth, sixth, and seventh have, 

 firstly, remained tubercular as in the dogs, or, sec- 

 ondly, have been lost, as in hyaenas and cats. 



The reduction of the number of molars in relation 

 to the increase in the size of the canines commenced 

 as early as the Jurassic period. It is seen in the gen- 

 era Triconodon (Owen) and Paurodon (Marsh), where 



