ON SKULLS OF HORSES FROM THE ROMAN FORT AT NEWSTEAD. 565 



of the face is also concave (PL I. fig. 5), but in the adult it is always decidedly 

 convex (PL II. fig. 7). This change, from a dished face to a "Roman-nosed" con- 

 dition, results in part from the bending of the face on the cranium, and in part from 

 the expansion of the frontal sinuses and the vertical increase of the nasal fossae. 



The difference in the outline of the skull between a Forest and a Steppe horse is 

 best realised by superimposing the outline of a " Roman-nosed " Prejvalsky horse on the 

 skull of a dish-faced horse of the Forest type. This, however, somewhat exaggerates 

 the difference between the facial outlines, because in the Steppe horse the face forms a 

 more marked angle with the cranium. In fig. 1 it is impossible to say where the 

 prominence due to the frontal sinuses ends and the elevation of the nasals begins ; but 

 in some cases either the frontal sinuses or the nasal fossae are unusually developed, with 

 the result that instead of an even contour there is a marked prominence either above 

 or below the level of the orbits ; in other cases both frontal sinuses and nasal fossae are 

 unusually large, with the result that there are two distinct prominences which give an 

 extremely sinuous facial outline. 



Prominent frontal sinuses and large upward extensions of the nasal fossae have only 

 been observed in horse skulls of the Steppe type, i.e. in skulls in which the face is very 

 long and bent downwards. In the Kiang — a form which occurs up to a height of 

 15,000 feet — the nasal fossae are also very extensive. It is hence possible that the 

 great size of the nasal chambers is a special adaptation for a life in cold, mountainous 

 areas. In horses living in cold regions, the moisture is in great part removed from the 

 air by coming into contact with short, stiff hairs which stretch across the narrow 

 nostrils ; the air having got rid of some of its moisture at the nostrils, the large nasal 

 fossae may admit of its temperature being somewhat raised before it passes on to the 

 lungs. 



The Newstead skull (PL II. fig. 7) of the Steppe type not only differs from the 

 skull of the Forest type (PL II. fig. 6) in having the face bent, it also differs in the 

 cephalic and frontal indices. In length the cranium is 165 mm., in width 96 mm. — 

 i.e. though in its total length 13 mm. longer, the cranium is 11 mm. narrower than in 

 the skull of the Forest type (Table I.). In the latter the cephalic index is 67 '29, 

 in the Steppe-like skull it is only 58*18. Moreover, the two crania differ in shape ; 

 in the one (the Steppe skull) the sides of the cranium are flattened, whereas in the 

 Forest skull the sides of the cranium are rounded and prominent.* 



Compared with the Forest skull the 560 mm. Steppe skull has a very long face — it 

 measures 399 mm. (26 mm. longer than the face in the Forest skull) by 223 mm., the 

 frontal index being 50*33, or 10*96 less than in the Forest skull. The great length of 

 the face has partly resulted from a backward shunting of the articular surfaces for the 

 mandibular condyles. One result of this shunting is a diminution of the post- orbital 



* The cranium of the skull represented in PI. II. fig. 7, is probably abnormally small ; perhaps small-brained 

 members of the Steppe variety were more easily domesticated than individuals with a large brain, such as normally 

 occurs in the recent Steppe horse, E. prejvalskii. 



