ORIGIN OF THE HORSE. 9 



four toes in front, the fourth disappearing, and 

 three only behind. In Mesohippus there are but 

 three toes, the fourth being represented by a 

 splint. In Miohippus there are also three toes 

 and a very rudimentary splint, the second and 

 fourth toes disappearing, thus leaving this an- 

 cestor of the horse to walk on his third or middle 

 toe. In Protohippus the second and fourth toes 

 are smaller still. In Pliohippus these toes are 

 represented by splints, which in a still more 

 rudimentary form exist to this day. 



In Pliohippus we see the first real soliped or 

 solid-footed animal in this descent, and the ani- 

 mal was distmctly of a horselike type. Thus 

 may we trace the evolution of the one-toed horse 

 from his five-toed ancestor. Besides the splint 

 bones we have in further evidence of this evolu- 

 tion from a soft-footed ancestor the footskin 

 which entirely covers the soft structures of the 

 horse's foot from the horny box which protects 

 them — the hoof, which was evolved to withstand 

 the resistance of the hardened ground. There 

 are various other proofs of the descent as out- 

 lined, but these need not be dealt with here. 

 There are some other intermediate links, but 

 the line followed gives the main steps in the 

 evolution of the horse as arranged by Marsh. 



Pliohippus was prevalent in all the great con- 

 tinents. How the horse was extinguished in 

 America we do not know. It was, however, in 

 Asia south of the Altai Mountains in Mongolia, 



