THE PEJEVALSKY HORSE. 27 



(eight out of twelve) gave the same proportion between tlie two 

 diameters as does the skull of the horse ; the others resembled 

 the ass. In one specimen of E. hemionus the two distances were 

 equal. 



In this region, the skull of the hinny (E. hinnus) is remarkable. 

 Transverse measurements of the nasal bones, such as have been 

 discussed above, give figures which indicate an exaggeration of 

 the ass type of skulL The anterior transverse measurement ex- 

 ceeded the posterior by some 14 mm. ; whereas, in the ass, the 

 difference did not exceed 9 mm. Then, the difference between the 

 leng-th of the nasal bone from the highest part of the naso-frontal 

 suture and the length along the inter-nasal suture reached 49 mm. 

 — a very unusual figure for the horse. Again, the conformation 

 of the lachrymal bone and the shape of the naso-lachryinal sutvire 

 were of the ass type. Therefore, the skull of the liinny is inter- 

 mediate between the skulls of the horse and the ass ; inasmuch 

 as the difference between the transverse measurement from the 

 anterior and posterior ends of the two naso-lachrymal sutures 

 resembles that common in the ass, while the form of the posterior 

 part of the nasal bones and of the naso-lachrymal suture correspond 

 to the horse. 



In shape, the post-orbital process of the frontal bone (processus 

 zygomatici ossis frontalis) is three-sided in the horse and flattened 

 in the ass. Essentially, however, the process, in both the horse 

 and the ass, consists of a bony plate, one edge of which curves 

 downwards. Upon the degree of this curvature depends the 

 greater or lesser three-sided character of the process. I am con- 

 vinced that the shape of the post-orbital process is in no way 

 distinctive of the various species of Eqinis, and shall, therefore, 

 discuss it no further. 



The basilar length and the length of the vertex of the skull of 

 E. jirjevaUJiu varied very little. In five specimens the shortest 

 basilar length Avas 472 mm., and the longest 495 mm. — a difference 

 not exceeding 5^ per cent, of the total length. This is much less 

 than in the onager, where the difference amounted to 10 per cent. 

 In E . j)r jevaWkii the average basilar length of the skull was 483 

 mm. : in the onager it was 453 mm. The amount of variation 

 in this diameter in the domestic horse is considerably greater. 

 The smallest skull of the ordinary horse which I measured had a 

 basilar length of 428 mm. (No. 4,049) ; while the skull of a Kirghiz 

 horse had a length of 498 mm. This difference — one of 15 per 

 cent. — was quite naturally to be expected when domesticated horses 

 were being dealt with. Among the skulls examined was one of 

 a Somaliland ass (E. aslnus var. somalicus) of an unusually large 



