THE EVOLUTION THEORY 



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As proved by many fortunate finds made in the Tertiary 

 strata of Europe, supplemented afterwards by more complete 

 discoveries made in North America, the horse has descended 

 from ancestral forms which possessed a much more complete 

 hand and foot skeleton and closely resembled the tapir. The 

 oldest ancestors of our horse may be traced to the deepest 

 Eocene strata. Here we find the genus Hyracotkcrium, little 

 animals about the size of a fox. They probably lived together 

 in large herds. The anterior extremities of Hyracotherium had 



PIG. 29. DEVELOPMENT OF THE FOOT OF THE HORSE. 



(1) Anterior foot of Hyracotherium (Eocene) ; (2) of Mesohippus (Lower Miocene) ; 

 (3) of Anchitherium (Middle and Upper Miocene) ; (4) of Hipparion (Pliocene) ; 

 (5) of Horse (Eqiius) (modern). (After v. Zittel and Kayser.) 



still four, the posterior three well-developed toes. In the later 

 strata this form is replaced by the three-toed Palacotherium, an 

 animal partly tapir, partly rhinoceros, about the size of a pony. 

 In the Miocene strata we find at the bottom the so-called 

 Mesohippus of the genus Palceotherium, and in the higher strata 

 the Anchitherium. These animals are still three-toed, but the 

 middle digit is already much larger than the other two and 

 almost exclusively supports the weight of the body. 



The retrogressive process becomes still more complete in the 

 Hipparion in the Pliocene strata, the youngest of the Tertiary 

 Period. In these animals the equine type is complete, the only 

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