26 THE PRJEVALSKY HORSE. 



convex instead of concave. In the Asiatic ass (E. hemionus), the 

 form of the suture resembles that of the donkey, and its curvature 

 is occasionally very decided. In E. ijrjevahMi the suture is like 

 that of the horse. 



In both tlie horse and the ass, the nasal bone consists of a broad 

 posterior part, and a narrow anterior portion. In the ass the 

 bone narrows rapidly anteriorly ; but in the horse the narrowing 

 is gradual. The nasal bones of the ass may, therefore, be described 

 as club-shaped ; and those of the horse as wedge-shaped. The form 

 of tlie posterior part is not the same in the horse and the ass. 

 In the horse the nasal bones project into the frontal in the form 

 of two large convex lobes. In the ass the lobes are smaller, and have 

 a less pronounced convexity (Fig. 7) : in some individuals, indeed, 

 they are bounded by an almost straight line. In the horse, conse- 

 quently, the naso-frontal suture has the form of two fairly high 

 arches, joined together in the middle line of the skull ; whereas, 

 in the ass, it is in the form of two almost straight lines meeting 

 in the middle line at an angle. For the purpose of demonstrating 

 the shape of the nasal bones by measurements, I decided to take 

 their width and length. I made three measurements of their 

 width : first, from the posterior and most external point on the 

 naso-lachrymal suture (Figs. 6 and 7, a) ; the second, from the 

 anterior and most external point on this suture (Figs. 6 and 7, h) ; 

 and the third from the point of contact of the intermaxillary and 

 nasal bones (Figs. 6 and 7, c). The leng'th of the bones was 

 measured in two directions. The first diameter was taken from the 

 highest point on the naso-frontal suture to the apex of the nasal bone 

 (Figs. 6 and 7, d to e) ; and the second along the entire length of the 

 suture between the two nasal bones (Figs. 6 and 7, f to e). The 

 figures thus obtained exhibit fairly marked differences between the 

 skulls of the horse and of the ass. In the horse the distance between 

 the posterior ends of the two naso-lachrymail sutures is greater than 

 that between their anterior ends ; that is to say, the posterior part 

 of the nasal bone of the horse narrows anteriorly. In the ass 

 the reverse is the case ; that is, the nasal bones increase in width. 

 This condition was found to be very constant in the skulls of 

 eleven horses and five asses. In only one horse's skull (No. 2.306) 

 was there an equality in the two diameters ; whereas, in the other 

 specimens there was a difference of from 5 to 10 mm. In the ass 

 the more anterior measurement was greater than the posterior 

 by from 5 to 8 mm. In this character, the representative speci- 

 mens of E. prjevahshii were in complete agreement with E. 

 cahallus. As in regard to Franck's index, so here the Asiatic 

 wild ass shows variations. The majority of the skulls examined 



