KINE TO GENESIS. 



323 



superior molars {if). 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; 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 



-•e 



...e 



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

 transition from bunodont (A) type to lophodonts [B, C). A, Sus erytnanthius. 

 B, Ovis amaltheus. C, Bos taurus. From Gaudry. Letters : d, 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 



