THE ANCESTRY OF THE HORSE 169 



the toes were not the only changes that were 

 required to transform the progeny of the Hy- 

 racothere into a horse. These are the most 

 evident ; but the increased complexity in the 

 structure of the teeth was quite as important. 



of the Horse. 



The teeth of gnawing animals have often been 

 compared to a chisel which is made of a steel 

 plate with soft iron backing, and the teeth of 

 a horse, or of other grass-eating animals, are 

 simply an elaboration of this idea. The hard 



