14 .i.\//<;A7r.i.v Ml s/a.M criDi': ij^aflkts 



is i)i()l)al)l(' thai in some biccds there is a ('onsidcral)!^ strain of tliis 

 slia^^y, sh()it-l('<i;^(Ml iMiropcaii race. The doincsticated ass is a do- 

 scciidanl of the wild ass ilujuus (isinus) of Xoi'th Afi-ica. 



THE EVOLUTION OF THE HORSE 



^r^HI'] histoiy of the evolution of the horse through the Teitiary 

 I Period or A<:;e of Manunals affords the best known illustration of 

 the doctrine of evolution by means of natural selection and the 

 adaptation of a race of animals to its enviionment . The ancestry of this 

 family has been tiaced back to near the beginninj^ of the Tertiary with- 

 out a single important break. Durinj>; this lonji; period of time, estimated 

 at nearly three millions of years, these animals passed through important 

 changes in all j)arts of the body, but especially in the teeth and feet, 

 ada})tin^ them more and more perfectly to their particular environment, 

 namely the open plains of a great plateau region with their scant}^ 

 stunted herbage, which is the natural habitat of the horse. 



In the series of ancestors of the horse we can trace every step in the 

 evolution of those marked peculiarities of teeth and feet w^hich distinguish 

 the modern animal from an ancestor which so little suggests a horse that 

 when its remains wTre first found forty years ago. it was named by the 

 great palaeontologist Richard Owen, the Hyracotherium or ''coney-like 

 beast." Its relation to the horse was not at that time suspected by Pro- 

 fessor Owen, and was recognized by scientific men only when several of 

 the intermediate stages between it and its modern descendant had been 

 discovered. On the other hand this first ancestor of the horse line is ver}- 

 difficult to distinguish from the contemporary ancestors of tapirs and 

 rhinoceroses, and indicates how all the modern quadrupeds have diverged 

 from a single type, each becoming adapted to the needs of its especial 

 mode of life. 



FOUR-TOED HORSES 



THE earliest known ancestors of the horse were small animals not 

 larger than the domestic cat, with four complete toes on each fore 

 foot and three on each hind foot. There is reason to believe that 

 still more ancient ancestors of this and all other mammals had five toes 

 on each foot. In the fore foot of the earliest known stage there way have 

 been a small, slender rudiment representing the missing first digit or 

 thumb, which no longer appeared on the surface of the foot,^ while in the 

 hind foot there is a similar rudiment representing the outer or fifth digit, 



'It is shown in Marsh's well known (liaKniin; hut there is no conclusive evidence of its presence 

 on any specimen yet found. 



