observed that Eohippus and the skull are of about the same length; 



also that one feature of equine evolution is a continuous increase in size. 



This principle of continuous increase in size is graphically displayed 



in the wonderful SERIES EOCENE TO OLIGOCENE representing 



~ff a ^~ 

 the first five or six stages in the evolution of the horse, where tm-ee 



principles are at once apparent: first, increase in size; second, increase 

 in length and delicacy of limb; third, elongation of the limb below 

 the knee joint and hock joint; fourth, disappearance of the outer 

 hoofs, and concentration on the median hoof which now begins to 

 rapidly increase in size. 



SKELETONS OF WHIPPETT AXD OF EOHIPPUS 



These steps are wonderfully displayed in the series of horses begin- 

 ning with Eohippus on the left and ending with Mesohippus on the 

 right, representing a transformation which occupied perhaps a period 

 of eight hundred thousand to one million years, through natural proc- 

 esses of breeding and the increasingly severe competition of these 



[ 23 ] 



