KINE TO GENESIS. 



323 



superior molars {a). The mutual interaction and effect 

 on the form of the crescents may be readily under- 

 stood. In Fig. go the successive stages of this effect 



Fig. gi — Two true molars of both jaws of a ruminant : a, superior molars, 

 their inner crescents ; b^ inferior molars, their external crescents ; the arcs 

 show directions of motion of jaws in mastication ; from Ryder. 



on one or two cusps may be seen, beginning with a 

 cone {a) and terminating with crescents {ef). Thus is 

 the origin of the selenodont dentition of the highest 



Fig. 92.— Transverse vertical sections of superior molar teeth, showing 

 transition from bunodont (A) type to lophodonts (5, C). A, Sits erymanihius. 

 B, Ovis amaltheus. C, Bos iaurus. From Gandry. Letters : li, dentine ; e, 

 enamel ; c, cementum. 



artiodactyle explained by Ryder, and, I believe, cor- 

 rectly. 



Kowalevsky and I have shown that the types with 

 selenodont (crescent- bearing) molars, have descended 



