ARABS AND THOROUGHBREDS. 21 



limbs the shaft of the uhia, or small bone of the lower part of 

 the fore-leg, is complete ; the cannon-bones are elongated and 

 slender ; and the jmsterns are long and sloping. Desert-bred 

 Arabs are stated to have denser bones than ordinary Horses. 



Despite the fuct that a complete ulna has been observed in a 

 skeleton of Grevy's Zebra, the whole of the foregoing characters 

 are regarded by Prof. H. F. Osborn [Bulletin of the American 

 Museum of Natural History, vol. xxxiii, pp. 259-263^ 1907) to 

 justify the specific separation of the Arab Horse^ for which he 

 adopts Sanson's name of Equus africanus.'^ The origin and 

 descent of the Arab are considered by the same observer to be 

 totally different from those of the Northern Horse. 



As regards the extent to which the facial part of the skull is 

 bent down on the basal axis, there appears to be some amount of 

 variation among Arabs and Thoroughbreds; but the feature is 

 always developed in a considerable degree. It also occurs in the 

 skull of the extinct Equus sivalensis as is shown by a cast 

 (N.H. 42) in the north side of the table-case. 



This marked bending-down of the face in Equus sivalensis, 

 coupled with the presence of a distinct remnant of the preorbital 

 face-pit in the skull and the above-mentioned characters of 

 the dentition, indicates the essential distinction of that species 

 from the Mongolian Wild Horse, which, as already mentioned, 

 is regarded as the survivor of the ancestral type which gave rise to 

 the ordinary Horses of North-western Europe. And since several 

 of the features characteristic of Arabs and Thoroughbreds are 

 met with in Equus sivalensis, there seems a probability that the 

 latter (or some closely allied race) may have been the ancestral 

 stock from which Barbs, Arabs, and Thoroughbreds are derived. 

 At any rate, this theory seems to afford a better working 

 explanation of the facts of the case (so far as they are at present 

 known) than any other hitherto suggested. If the Arab Horse 

 should ever be proved to be descended from a species distinct 

 from the one which gave rise to the Wild Horse of Mongolia, it 

 will, of course, have to bear a name other than Equus cahallus. 



* See note page 17. 



