560 PROFESSOR J. C. EWART 



and, it may be added, by comparing the measurements of skulls of different ages, and 

 by taking the average of skulls belonging to different varieties, real and essential 

 differences are almost inevitably lost sight of. 



In the case of human skulls it is especially important to determine the cephalic 

 index, i.e. the relation of the breadth to the length of the cranium, the length beino- 

 taken as 100. But as, for various reasons, the skulls of horses differ from each other 

 in the facial more than in the cranial portion, measurements of the face are in their 

 case especially important. 



About the horse, we especially want to know (1) what relation the width of the 

 face bears (a) to its length, and (6) to the length of the base of the skull ; (2) to 

 what extent the face is bent downwards on the cranium ; and (3) to what extent the 

 outline of the face is modified by the development of frontal sinuses, and by an increase 

 in the vertical extent of the nasal fossae. 



In the human skull there is no difficulty in deciding where the cranium ends and 

 the face begins ; but in the horse it is so difficult to say where the face begins that at 

 least three ways have already been suggested for obtaining the length of the face, and 

 I have found it necessary to introduce a fourth. 



Czerski, to obtain the length of the face, measured from the central incisors to the 

 anterior border of the orbit. Salensky, # recognising that the anterior border of the 

 orbit does not coincide with the junction of the cranium and the face, measured from 

 the central incisors to the point of union of the frontal and nasal bones, i.e. to the 

 posterior end of the internasal suture. But as the end of the internasal suture does 

 not at all coincide with the end of the cranial cavity, and as the line of the naso-frontal 

 suture varies considerably — extending further along the face in some cases than in 

 others — I decided to obtain the length of the face by measuring from the central 

 incisors (the alveolar point) to a line connecting the posterior borders of the orbits. 

 This line coincides almost exactly with the most anterior portion of the cranial cavity. 

 The width of the face is best arrived at, as Nehring recognised, by measuring between 

 the outer margins of the orbits. This (the frontal width) multiplied by 100 and divided 

 by the facial length gives the frontal index. 



The extent to which the face is bent downwards on the cranium is made evident 

 when outlines of photographs of side views of skulls are placed one above the other, 

 and when the angle formed by the line of the palate and the basi-cranial axis is given. 

 The difference between a bent skull in which the frontal sinuses and the nasal fossae 

 are highly developed and a skull with a concave facial outline, is best indicated by 

 adding to a photograph of a dish-faced skull the facial outline of a skull of the " Roman- 

 nosed " type. 



If, as seems probable, the remote three-toed ancestors of the Equidse were adapted 

 for a forest life, it may be assumed that the variety now most richly striped, and 



* The methods of Czerski, Nehring, and others for measuring horse skulls are described in Salensky's work 

 on Prejvalsky's horse. Translation by Hayes & Bradley. Hurst & Blackett, 1907. 



