28 THE PEJEVALSKY HOESE. 



size. The enormous size of the head of the Somaliland ass is well 

 known. In the ass the basilar len^h varied from 362 to 373 mm. ; 

 but in the Somaliland ass it was 450 mm. The variation in the 

 length of the skulls of individual asses may be very considerable, 

 and is probably due to racial differences. In this connection it 

 may be mentioned that Nehring * gives measurements of the skull 

 of a Maltese donkey which had the enormous length of 504 mm. ; 

 while the length of the skull of the domestic ass (E. asinus), accord- 

 ing to the same writer, varies from 353 to 393 mm. Here is 

 evidently a racial peculiarity. 



In the skull of E. prjevahkii the length of the vertex varies 

 even less than does the basilar length ; namely, from 528 to 547 

 mm. — corresponding to less than 4 per cent, of the greatest length. 

 In the Asiatic ass the range of variation is greater, namely, from 

 487 to 529 mm. In the domestic horse, if we include the skulls 

 of sub-fossil horses, the range was still greater, namely, from 506 

 to 565 mm. The greatest lengtli was reached by the skull of a 

 Kirghiz horse (No. 1,988), an animal distinguished by a very large 

 and somewhat convex head. In E. i^rjevahhii the average length 

 of the vertex of the skull was 539.8 mm. ; in the onager 509 mm. ; 

 in the kiang 524 mm. ; and in the domestic horse 524 mm. From 

 this it is evident that the Prjevalsky horse has a very large head ; 

 a peculiarity all the more striking because of the circumstance that 

 the body is smaller than that of many breeds of domestic horses. 



The relation of the length of the base of the skull to the length 

 of the vertex depends upon the degree of curvature of the skull 

 a.s a whole, and is expressed by the difference between the length 

 of the vertex and the basilar length. In the Prjevalsky horse this 

 diffei'ence is subject to relatively little variation ; namely, from 52 

 mm. (No'. 3,074) to 62 mm. (No. 3,094). In this respect the 

 Prjevalsky horse resembles the Asiatic ass, in which the difference 

 varied from 51 to 70 mm. ; while in the domestic horse it ranged 

 from 37 to 67 mm. The maximum difference (67 mm.) belongs 

 to the extremely convex skull of the Kirghiz horse ; so that, if we 

 exclude this specimen, the variation in the domestic horses is only 

 from 37 to 57 mm., and, therefore, does not exceed the range in 

 the Prjevalsky horse and in the Asiatic ass. 



In E. 2yjevaIsJiii, the average frontal width was 206 mm. ; and 

 the range of variation was from 201 to 212 mm., which is not 

 very great. The broadest forehead (212 mm.) was found in a 

 specimen, sent by Schischmareff from Kobdo, in which it is remark- 

 able that the skull as a whole is by no means a long one. In frontal 

 width E. prjevahkii differs in a well marked manner from E. 

 * Op. cit. p. 103. 



