234 



GEOLOGY. 



The distinction is not so much a matter of toes as of mode of support. 

 In the odd-toed, the main line of support lies in the axis of the middle 

 toe (Memxonia) ; in the even-toed, it lies between the third and fourth 

 toes (Paraxonia) ; in other words, one main line of support in the first 

 case, and two in the second. In the course of time, the lateral toes fell 



d e f 



Fig. 430. — Comparison of brains. Eocene brains: a, Coryphodon hamatus; b, 

 Tinoceras pugnax. Miocene brains: c, Eporeodon sociates; d, Elotherium crassum. 

 Pliocene brain: e, Platygonus compressus. Modern brain: /, Auchenia vicugna. 

 (After Marsh.) 



out of use and were atrophied. The first class reached its extreme type 

 at length in the horse, and the second in our cloven-hoofed cattle. But 

 these perfected types were not attained in this period, which only wit- 

 nessed the initial divergence. The original five spreading toes were not 

 so advantageous on hard, grassy ground as a strong, concentrated line 

 of support through the center of the foot, and as the toes were no longer 



