()1)s('1-v(m] tliat Eohippus and the skull arc of al)()iit the same length; 

 also that one feature of eciuine e\-()lution is a eontinuous increase in size. 

 This |)rinci])le of continuous inci'case in size is <i;ra|)iiicaliy displayed 

 in the wonderful SKRIES EOCENE TO OLIGOCENE representing 

 the first five or six stages in the evolution of the horse, where three 

 ))i'inciples are at once ajiparent: first, increase in size; second, increase 

 in length and (lelicac\- of liinh; third, elongation of the limh l)elow 

 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. 



SKKl.KTONS OF Wll I IM'KTT AMJ OF KOlllPl'lS 



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

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

 right, representing a transformation which occupied i)erhaps a period 

 of eight hundr(>d thousand to one million years, through natural proc- 

 esses of l)re(\ling and the inci-easingly severe competition of these 



I OA I 



