EVIDENCES OF EVOLUTION 25 



pus, with four toes in front and three behind, 

 the side ones behind touching the ground. It 

 seems to have been about fourteen inches 

 high, and the evolution of speed had begun. 

 During the Eocene times North America was 

 in great part forest-clad, but 'the moist 

 climate gave rise to many streams and lakes, 

 along the shores of which grew sedgy mead- 

 ows that in turn gave rise to grassy plains. 

 These were the conditions under which the 

 horses made their first appearance, and the 

 increasing development of grass lands gave 

 the initial trend to their evolution.' 3 



Somewhat later, in the Oligocene, Meso- 

 hippus makes its appearance, the hind-foot 

 with three toes as before, but the fore-foot 

 with the little toe reduced to a splint, so that 

 only three remain, the side ones just touch- 

 ing the ground. The middle or third toe is 

 now much larger than the side toes, which no 

 longer bear much of the weight of the animal, 

 save on marshy ground. The grinding teeth 

 have become more complex. One of the 

 species of Mesohippus was about the size of 

 a sheep, and one of the treasures in the Yale 

 Museum that brings the past very vividly 

 back to us is the nearly perfect skull of its 

 new-born foal. Of the physical conditions 

 of the Oligocene, Dr. Lull writes: ;4 The dry- 

 ing up of streams and lakes, due to the 



