KINETOGENESIS. 339 



mastication is added to the sectorial in some Creodonta, 

 and in CanidaB and Ursidae, etc., among Carnivora. 

 This function predominates over that of the anterior 

 triangle in the Lemuridae. (Fig. 95.) 



I have already pointed out the successive modifica- 

 tions of form which have resulted in the existing spe- 

 cialized single inferior sectorial tooth of the Felidae. 

 They consist in the gradual obliteration of the poster- 

 ior-internal cusp, and of the heel, and the enlargement 

 of the external and anterior internal tubercles of the 

 primitive triangle. The modification in the character 

 of the dentition taken as a whole was shown to consist 



Fig. \vz.-Stypholophus whztite Cope ; diagram representing the apposition 

 of the inferior and superior molars. The superior are in light, the inferior 

 in heavy lines. The numbers represent the molars and premolars : C, canine; 

 poc, protocone; pac, paracone; me, metacone; POC, protoconid; PAC, para- 

 conid ; MC, metaconid ; he, hypocone ; HC, hypoconid. 



in the reduction of the number of the teeth, including 

 the sectorials, until in Felis, etc., we have almost the 

 entire function of the molar series confined to a single 

 large sectorial in each jaw. 



The genesis of the superior sectorial tooth has 

 been explained as follows. In consequence of the 

 fact that the lower canine tooth shuts anterior to the 

 superior canine, the result of the enlargement of the 

 diameters of those teeth will be to cause the crowns 

 of the inferior teeth to be drawn from behind forwards 

 against those of the superior teeth when the jaw is 

 closed (Fig. 102). Thus a shearing motion would re- 



