MOLAR TEETH OF THE MAMMALIA EDUOABILIA. 259 



Superior molar of 

 Equus. 



US the Selenoclont type of superior molars again in this genus ; 

 while the lower molars only diifer from that type in having the 

 crescents alternate instead of opposite, forming the Hippodont 

 pattern (Fig, 40). There can be little doubt that the line of the 

 horses comes through Hipposyus* from, the Bunodonts, rather than 

 through PalcBotherium, as has been sug- 

 gested by some writers. 



6. BaiJimodont type. — I know of no ge- 

 nus which by its iiitermediate structure 

 connects this type of molar with the Amce- 

 bodont form of Bunodonts.f Such will 

 doubtless be discovered, for it is impossible 

 that the upper molar of Bathmodon could 

 have been produced by the modification of 

 any known Palaeotheriodont, the type which 

 it most nearly resembles. The structure of 

 the feet of the animal forbids any such sup- 

 position. Such intermediate types would 

 have, firstly, the (oblique) crests more nearly 

 equal in length and similar in direction. A 

 depression of the crests and indication of 

 diagonal ridges connecting the tubercles in 

 the opposite direction would produce an 

 approach to a W, and the form of Hyopso- 

 dus. That this was probably the history 

 of this curious type is rendered probable by 

 the form of the mandibular teeth, which exhibit two of the in- 

 termediate stages above anticipated. Thus the last inferior molar 

 exhibits two obliquely transverse crests of subequal length, with 

 rudimental oblique or diagonal ridges connecting them. In the 

 median lower molars one of the latter is developed, giving a V, 

 as in Palceotlierium, but the posterior one is undeveloped, leaving 

 only the original oblique cross-crest. J 



7. The Loxolophodonts. — Like the preceding group I know 

 of no type connecting this form with the Bunodont, but antici- 

 pate the discovery of a type with a rudimental posterior V on the 



Fig. 40.- 



Inferior molar of 



Equus. 



* I have since shown tliat Hyracotherium and Pliolophus, which have very 

 similar dentition, are the types which occupy this position. (Ed. 1886.) 



\ Such has since been discovered in the genus Pantolambda (Cope). (Ed. 1886). 



X Sec " Proceed. Amcr. Philosophical Society," Sept., 1872, " On the Dentition of 

 Metalophodon." 



