410 



EVIDENCES OF EVOLUTION 



into several distinct species. Some of these remained in 

 North America and became extinct during the Ice Age. 

 Others migrated into South America where they died out 

 in very recent times. Still others travelled into the Old 

 World and became the ancestors of the modem breeds. 

 There were no horses in the New World when Columbus 

 made his voyages. 



Throughout this entire period the body was undergoing 

 many changes. Among the most obvious were those 

 affecting the feet. The middle digit gradually increased 

 in size, while the others became rudimentary or dis- 



II in W 



Fia. 120. — Evolution of the Hand of the Horee. 



appeared completely (Fig. 120). The result is that the 

 modern horse travels on the tip of a single (the middle) 

 digit, the hoof representing the nail, while the " knee " 

 is actually the wrist or ankle. The teeth also became 

 modified, and as a result of these and other changes the 

 generalized five-toed ancestor evolved into one of the 

 most highly specialized of modern animals. 



Evolution of Camels. — Although these animals are 

 not included in the list of native North American species, 

 the family actually passed through the greater part of 

 its development on this continent. The earliest known 



