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. 91 Two true molars of both jaws of a ruminant : a, superior molars, 

 their inner crescents ; f>, 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 



....e 



C-H 



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

 transition from bunodont (A] type to lophodonts (B, C). A, Sus erymanthius. 

 B, Ovis amaltheus. C, Bos tatirus. From Gaudry. Letters : d, dentine ; e, 

 enamel ; <r, 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 



