THE PEJEVALSKY HORSE. 21 



whole skull (Length of the vertex). These relations he indicated 

 by his Index I. and Index II. The length of the skull is measured 

 (1) along its base from the lower border of the foramen magnum 

 to the base of the middle incisor teeth (Basilar length of the 

 skull), and (2) from the edge of the occipital crest along the exter- 

 nal upper surface of the skull to the base of the middle incisor 

 teeth (Length of the vertex of the shuU ). In taking the height 

 of the skull, Nehring included the lower jaw. Such a measurement 

 is not satisfactory, because the lower jaw is liable to considerable 

 variation which would naturally influence, to a great extent, the 

 total measurement ; wliereby no exact idea of the height of the 

 real cranial box could be conveyed. It is, therefore, better to 

 follow the example of Czerski and add a diameter of the height 

 of the cranium, measured from its base to the summit of the 

 occipital crest. I have adopted such a measurement in my own 

 observations. 



Nehring determined the position of the orbital cavitj^, as I'egards 

 the lateral surface of the skull, by means of two measurements 

 which, taken together, constitute his Ocular line (Augenlinie). 

 These are as follows : (1) from the occipital crest to the most ex- 

 ternal point on the posterior border of the orbital cavity (posterior 

 segment of the ocular line) and (2) from the most external part 

 of the posterior border of the orbital cavity to the base of the 

 middle incisor (anterior segment of the ocular line). If the 

 posterior segment of the ocular line be taken as 100, the relation 

 of its length to that of the anterior segment gives Nehring's 

 Index III. — Ocular index (Augenindex). 



Respecting Nehring's ocular line, Czerski * correctly remarks 

 that it gives no idea of the proportion which the facial part of 

 the skull bears to the cranial part. In order that his measure- 

 ments might indicate the ratio between the length of the face and 

 the length of the cranium, Czerski added another diameter, taken 

 from a point between the central incisor teeth to the nearest part 

 of the anterior border of the orbital cavity. From the relation 

 of this diameter to the basilar length of the skull he computed a 

 Facial index. Although in entire agreement with Czerski regard- 

 ing the necessity for some expression of the ratio of the cranial 

 part of the skull to the facial part thereof, I do not find that his 

 index is satisfactory. And for these reasons : (1) because the an- 

 terior border of the orbital cavity does not coincide with the 

 junction of the cranium and face, and (2) because the parietal 

 measurement is referred by Czerski to the basilar length. The 

 relation of the parietal length of the skull to its basilar length 



* Op. cit. p. 378. 



