Part I. EVOl.UTION OF TU\l HORSH IN NATURE 



By W. I). Matthew, Ph.D. 



Curator, 1 )c|)art lucnt of XCiiclnalr I'alatttitoloj^y 



INTRODUCTION 



As a (loinostic animal tlu^ lu)i's(Ms to he louiid mIiiiosI cvciAwhcrc lli;il 

 / \ man can live. II(' is si)i(>a(l all ovci- the world rrom torrid id 

 arctic climates, in all the continents, in i-emote oceanic islands 

 he is completely cosmopolitan. Hut as a wild animal tlie horse is at 

 present limited to the Old World, and is found theic only in llie open aiid 

 or desert plains of Central Asia and Africa, 'i'here are. two species in 

 Asia, the Asiatic wild ass {Equus hetnionus) and the little known I^rze- 

 walsky horse {Equus przeivalskii), while in Africa there are the African 

 wild ass {Equus asimis) and the several spcH'ies of zebra (E(/uiis zchra, 

 Equus hurcheUi, Equus grevyi). In the Americas and Australia there are 

 no true wild horses, the mustangs and broncos of the Western Plains and 

 South America being feral (domesticated animals run wild) and de- 

 scended from the horses brought over from Europe l)y the early white 

 settlers. When the Spaniards first explored the New World they fotmd 

 no horses on either continent. The Indians were quite unfamiliar with 

 them and at first regarded the strange animal w^hich the newcomers rode, 

 with wonder and terror, like that of the ancient Romans when Pyrrhu< 

 and his Greeks brought elephants — ''the huge earth-shaking Ix^asts" — ■ 

 to fight against them. 



The horse is distinguished from all other animals now living ))y the 

 fact that he has but one toe on each foot. Comparison with other animals 

 shows that this toe is the third or middle digit of the foot. The hoof 

 corresponds to the nail of a man or the claw of a dog or cat, and is broad- 

 ened out to afford a firm, strong support on which the whole weight of the 

 animal rests. Behind the " cannon bone " of the foot ai'e two slender lit t le 

 bones, one on each side, called ''sphnt bones." These represent the 

 second and fourth digits of other animals, but they do not show on the 

 surface and there is nothing like a separate toe. So that the hoi-se may 

 be said to be an animal that walks on its middle finger nail, all the other 

 fingers having disappeared. 



The teeth of the horse are almost equally peculiai'. Tlu^ molars are 

 long, square prisms which grow up from the gums as fast as the>' wear off 

 on the crowns. Their grinding surface exhibits a peculiar and compli- 

 cated pattern of edges of hard enamel between which are softer spaces 

 composed of dentine and of a material called ''cement," much like the 

 dentine in quahty but formed in a different way. The d(Mitin(^ is foruHMl 



