164 B. S. Lull— The Evolution of the Horse Family. 



inches high, known to science as Eohippus. This interesting- 

 animal has already made a long stride in the direction of the 

 modern horse, as the number of toes is now reduced to four in 

 front and three behind, and the bones of the wrist and ankle 

 have shifted so as to interlock, which greatly strengthens the 

 foot. 



The Evolutionary Changes. 



From the Condylarthra and Eohippus the course of evolu- 

 tion is largely one of adaptation to the necessities of food get- 



Fig. 3. a, Forefoot and b, hind foot of Phenacodus primcevus ; drawn 

 from easts from the American Museum of Natural History. One-third 

 natural size. (Original.) 



ting and safety. To the one the horse owes the marvelous 

 perfection of the grazing mechanism, as seen in the lengthened 

 jaws and in the teeth ; to the other, the fleet limbs and grace- 

 ful contour of the body and the increase in stature. These 

 adaptations are entirely mechanical, and, while tending toward 

 greater and greater perfection on the whole, are not always of 

 a progressive character; as the loss of side toes is distinctly 

 retrogressive. 



