Possible Ancestors of the Horses living under Domestication. 393 



browed, had a long, tapering, strongly deflected face ; a third (E. fossilis) had 

 a long, narrow face, not so strongly bent downwards as in E. sivalensis; and 

 a fourth ( E. gracilis) had a fine, narrow, but only slightly deflected, face. 



In E. gracilis the middle metacarpal (cannon bone) was so slender that the 

 length was seven and a-half times the width, while in E. robustus the length 

 of the metacarpal was sometimes only five and a-half times the width. 



Of these possible ancestors, the first three occur in Pliocene deposits, the 

 second three have only hitherto been found in Pleistocene deposits. 



Equus sivalensis, of the Siwalik deposits of Northern India, is the oldest 

 true horse known to science {i.e. the oldest one-hoofed horse with long 

 (hypsodont) molars), and, as it measured about 15 hands, it is the largest of 

 the Old World " fossil " horses. This ancient Siwalik horse was characterised 

 by long, fairly slender limbs, and a long, tapering face, deflected to form an 

 angle of nearly 20° with the base of the cranium. In addition to having 

 a large head, a convex profile, and long limbs, E. sivalensis seems to have been 

 characterised by a long neck, high withers, and a tail set on so high that the 

 root was well in front of the point of the buttock. Nothing is known of the 

 ancestors of the horse which suddenly made its appearance in Pliocene times 

 amongst the foot hills of the Himalayas, but it may be safely assumed that 

 E. sivalensis very decidedly differed from Pliohippus, the small " fossil " horse 

 of the late Miocene and the early Pliocene deposits of America, from which 

 some believe all the recent Equidse are descended. 



It used to be said that E. sivalensis could not be regarded as an ancestor 

 of domestic horses because of the shortness of the anterior pillar of the cheek 

 teeth. I find, however, that in some modern horses the anterior pillars are 

 decidedly shorter than in E. sivalensis, and that in some of the short-pillared 

 domestic horses the face is nearly as strongly deflected on the cranium as in 

 E. sivalemis. There is hence no longer any reason for assuming that this 

 ancient Indian species had no share in the making of domestic breeds. But 

 in the absence of a large and representative collection of skulls of domestic 

 horses it is impossible to say which modern breeds are indebted to the large- 

 headed, long-limbed race which in Pliocene times frequented the area to the 

 east of the Jhelum River, now occupied by the Siwalik Hills. 



Mr. Lydekker thinks E. sivalensis, or some closely allied race, " may have 

 been the ancestral stock from which Barbs, Arabs, and Thoroughbreds are 

 derived." When more skulls are available for study and when the phases 

 through which equine skulls pass during development and growth have, been 

 worked out, it will probably be ascertained that broad-browed horses with 

 a prominent interorbital region — a forehead convex from side to side as well 

 as from above downwards — and a long, tapering, strongly deflected face have 



