WILLISTON: RESTORAIION OF PLATYGONUS. 



Skull of adult male. 



The adult male skull differs 

 very strongly from that of the 

 adult female, in the more prom- 

 inent margins to the temporal 

 fossae, in the greater convexity 

 of the front, in the narrower and 

 deeper sinus between the squa- 

 mosal and the malar, in the more 

 nearly closed orbit, and espe- 

 cially in the strongly project- 

 ing inferior border of the malar 

 bone over the masseter fossa, 

 recalling the elongated process 

 in the same region in Elothcri- 

 iim, which one might suspect 

 is more or less of a sexual 

 character. The canines are 

 stouter and more divaricate, 

 and the " prenasal " bone con- 

 tinues the mesethemoid with- 

 out distinct suture into a stout, 

 thick ossification, forming a 

 conical protuberance in front 

 of the incisor teeth. In the 

 lower jaw, the most noticeable 

 peculiarity is the much stronger 

 and more protuberant flange, 

 with its sharper anterior angle. 



/'. leptorhinm- W. skull of adult male, frontal 

 aspect, one-third nattiral size. 



Skull of young. 



The skull of the young animal differs, as would be supposed, in its 

 less angular projections. The temporal ridges are rounded, and the 

 sagittal portion is shorter. The zygomatic arches are more nearly 

 vertical in position, and the fossa for the masseter is but little im- 

 pressed, without the projecting ridge of bone above it, so prominent 

 in the male, and distinctly indicated in the female. The glenoid 

 surfaces are more nearly as they are in Dicotyles, and the post-canine 

 diastema, both above and below, is relatively shorter. The milk 

 molars of the lower jaw are more elongated than the true molars. 

 The order in which the permanent teeth were cut appears to be 

 ini, 1)12, !iij, pmj, pin2, pmi. 



