22 THE PKJEVALSKY HOESE. 



is liable to great variation. For these reasons, I have taken a 

 facial length from the base of the incisor teeth to the point of 

 union of the frontal and nasal bones, and have compared this 

 diameter with the length of the vertex of the skull. The relation- 

 ship tlius obtained I have indicated in a Facial index, or Index 

 IV., in computing which the length of the face is taken as 100. 

 In this index I also include the relation of the length of the cranium 

 to the length of the vertex of the skull.* 



The orbital cavities were measured horizontally and vertically 

 In order to determine the width of the cranial part, of the skull, 

 I measured tlie distance between the most prominent points on 

 the parietal bones, and the distance across the narrowest part of 

 the skull, i.e., on a level with the root of the post-orbital process 

 of the frontal bone. In this way, the broadest and narrowest dia- 

 meters of the cranium were ascertained. In addition, the width of 

 the skull between the upper edges of the external auditory meati 

 was determined. In order to ascertain the width of the face. I 

 measured its broadest and narrowest parts in the manner suggested 

 by Czerski. 



Further measurements of the skull refer to the length of the 

 series of cheek-teeth, taken, naturally, only from the skulls of full- 

 grown horses in which the full complement of teeth was present. 

 Following Nehring's method, two measurements were made ; one 

 along the bases of the teeth, the other along their wearing-surfaces. 

 The height and length of the lower jaw were also ascertained by 

 Nehring's method. The height of the nasal region, in consonance 

 with the plan adopted by Czerski, was measured from the posterior 

 edge of the last molar tooth to the middle of the inter-nasal 

 suture. 



A very important matter in these craniological investigations 

 is the proportion which the distance from the foramen magnum 

 to the edge of the vomer bears to the distance from the vomer 

 to the palatine bone. Franck has indicated that this is different 

 in the skull of the horse and of the ass ; since, in the ass, the first- 

 mentioned distance is smaller than the second, whereas, in the 

 horse, the second is smaller than the first. Nehring, in general, 

 agrees with this view, but he found, in the skull of an African ass, 

 ihat relationship of the two distances which is held to be character- 

 istic of the skull of the horse. Nevertheless, these measurements 

 are very important as a fairly good indication of a characteristic 



* For this reason Index IV. is represented in the accompanying tables by two 

 numliers, an upper and a lower. The upper refers to the relation of the length 

 of the face as compared with the length of the vertex ; the lower to the length of 

 the cranium in the same comparison. 



