THE TEETH 449 



modern Carnivora. Why, for instance, were not the last molars 

 modified into sectorial teeth in these animals, as in the extinct Hyseno- 

 don and various Creodonta? The answer obviously is to be found in 

 the development of the prehensile character of the canine teeth. It 

 is probable that the gape of the mouth in the Hysenodons 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 indi- 

 cate. 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 Felidse, though more 

 effective in this respect than those of the Hysenodons. The usefulness 

 of a lever of the third kind depends on the approximation 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 behind forward in the history of carnivorous types. Thus it is 

 that the only accessible cheek teeth, the fourth above and the fifth 

 below, have become specialized as sectorials, while the fifth, sixth, and 

 seventh have, firstly, remained tubercular, as in the dogs, or, secondly, 

 have been lost, as in hysenas and cats." 



The above explanation of the evolution of the molar teeth has been 

 accepted as amply justified by palseontological evidence. Professor 

 Scott, however, gives a different history for the premolars, which it 

 is necessary for us to consider. To the following extracts from Pro- 

 fessor Scott's paper 1 I have added the diagrams K, L, M, N, O, P, Q, 

 R, S, T, U, in Fig. 370 : 



" The premolars do not display quite the same degree of constancy 

 in the order of succession of their component cusps as do the molars. 

 For this reason the fourth superior premolar [corresponding to the 

 third of the cat] will be taken as the standard. The primitive form 

 of the premolar is a simple cone, implanted by a single fang, which 

 is still preserved in several existing genera and which obviously cor- 

 responds to the protocone of the molars (Fig. 370, K). As early as 



the Puerco, however, we find that *- in every known genus is com- 



1 Proc. Phila. Acacl. Nat, Sci., 1892, pp. 405-444. 



29 



