Hind Foot 
Splints of 
2 and 4! digits 
Three Toes 
Side toes 
Three Toes 
Side toes 
Three Toes 
Splint of 5“digit. 
and Teeth like those of Monkeys etc. 
Four Toes 
Splint of 1% digit 
Side toes 
touching the ground; 
Splint of 5‘ digit 
Three Toes 
Side toes 
not touching the ground 
Three Toes 
_ 
— 
i) 
om 
cv) 
= 
—) 
= 
Hypothetical Ancestors with Five Toes on Each Foot 
Protohippus 
Mesohippus 
Hyracotherium 
During three millions of years, these animals passed through important changes especially in 
the teeth and feet, adapting them more and more’ perfectly to their particular environment, namely open plains with scanty stunted herbage 
78 



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Formations in Western United States and Characteristic Type of Horse in Each 
















WHITE RIVER | == 




Oligocene |- 
Eee s 
The history of the evolution of the horse through the Age of 'Mammals gives the best example in existence of the doctrine of evolution by means of natural 
Age of Man} Pleistocene —— 
Age of 
Reptiles 
selection and the adaptation of a race of animals to its environment. 
Quaternary 
0 

