THE PEJEVALSKY HOESE. 33 



ill the regions of the zygomatic ridges and of the incisor teeth ; 

 and (3) by its height as measured from the middle of the inter- 

 nasal suture to the last molar tooth. 



The face in the Prjevalsky horse is long, and bore a ratio to 

 the length of the vertex of the skull as 100:175-179.7. The 

 variation in the absolute figures of the measurements are much 

 more .important than the relative figures of Index IV. In E. 

 'prjevalshii the length of the face varied from 295 to 317 mm. 

 In the Asiatic ass, the maximum length was not greater than 298 ; 

 and Index IV. revealed a proportion of 100:193; thereby indi- 

 cating a much greater variation than in the Prjevalsky horse. 

 The Somaliland ass, endowed with a face of extraordinary length 

 (2S9 ram.), forms an exception to the asses in general, in which 

 the face is quite short. The maximum facial length in the asses' 

 skulls amounted to 239 mm. ; and Index IV. varied from 100 : 174 

 to 100 : 187. Variations in the index were much less marked in 

 the domestic horse, and were within 100 : 172 and 100 : 180. 



The width of the face is greater in E. jjrjevahJcii than in any 

 other species of Eqiius. The minimum in grown-up animals was 

 180 mm. ; and the maximum, 190 mm. Although the facial width, 

 on a level with the zygomatic ridge, amounted to as much as 195 

 mm. in other species, as for instance in the Asiatic ass, this was 

 exceptional. In the majority it did not exceed 172 mm. ; that is, 

 it did not attain to the minimum width of the face of E. 

 ■p7 jevalsMt. It is notewortliy that an onager from the Desert of 

 Gobi (No. 515), which had the greatest facial length, was by no 

 means conspicuous for the width of its face. The width of the 

 fac3 in the region of the incisor teeth — spoken of, for the sake o£ 

 brevity, as the width of muzzle in the accompanying tables — was 

 very characteristic in the Prjevalsky horse. It was considerably 

 greater than in the Asiatic and African asses, and varied from 

 70 to 76 mm. In this respect, the skull of E. jjrjevalshii resembles 

 the skull of the domestic horse, in which the diameter ranged from 

 61 to 75 mm. In the skulls of the onager, the maximum nasal 

 width was 67 mm. ; and in the African ass it did not exceed 55 

 mm., except in the Somaliland ass, where it attained to 66 mm. 



An investigation of the height of the face — as measured from 

 the posterior part of the last molar tooth to the middle of the 

 inter-nasal suture — demonstrated that it is a comparatively value- 

 less aid to classification. In the Prjevalsky horse it measured 

 fx'om 133 to 138 mm. ; in the onager from 124 to 139 mm. ; in 

 the donkey from 102 (No. 1,136) to 130 mm. ; and in the domestic 

 horse from 134 to 150 mm. On account of these great variations 

 — especially in the onager, donkey and domestic horse, and to a 



3 



