OF EVOLUTION. 



61 



we have still a full five-toed animal, the Phe- 

 nacodus, which is now generally recognized as the 

 earliest known progenitor of the horse tribe. 

 Correlatively with the progressive changes in 

 the structure of the foot, there are equally well- 



i. 



2. 



4- 



Successive stages in the development of the European h^se. 1. Palae- 

 otherium (Eocene) ; 2. Anchitherium (Miocene) ; 3. Hipparion (Pli- 

 ocene) ; 4. Equus (modern). 



marked modifications in the disposition of the 

 bones of the arm and leg, and in the form and 

 complexity of the grinding teeth, which are also 

 illustrated on the chart before you. 



