1906-7.] Observations on the Skull of Equus prjevalskii. 49 
TABLE III. 
Palate. 
E. prjevalsJcii. 
Celtic. 
Iceland. 
Length, 
252 
235 
236 
Breadth, ...... 
70 
64 
69 
Palatine index , . . . . 
27-77 
27-23 
29-23 
The form and position of the orbit has notoriously much influence upon 
the appearance of the head of a living horse ; even in a series of macerated 
skulls considerable differences can be detected on inspection. That there 
were differences in the orbits of the three skulls at present under con- 
sideration could be readily determined by the eye. The outline of the orbit 
of the Prjevalsky horse was much farther removed from a circle than was 
that of either the Celtic or Iceland skull ; this is demonstrated by the 
indices in the following table, where the maximum diameter of the rim is 
held as being equal to 100. The peculiarity of the shape of the rim in 
Equus prjevalskii depended largely upon the position of the articulation 
between the post-orbital process of the frontal bone and the zygoma. That 
the articulation in this skull was farther back than in the Celtic and Ice- 
land skulls may be shown in the following manner. The amount of the 
orbital rim formed by the squamous temporal bone is dependent on the 
position of the articulation. The farther forward the joint, the smaller 
the part taken by the squamous temporal in the formation of the orbit. 
In the wild horse the temporal formed 27 mm. of the rim ; in the Celtic, 
only 11 mm. ; and in the Iceland, 15 mm. 
Not only did the shape of the orbit differ in the different skulls; its 
relative position was also different. The figures below show that in the 
wild horse the orbit was relatively farther back in the head than it was 
in the others. 
TABLE IV. 
Orbit. 
E. prjevalsJcii. 
Celtic. 
Iceland. 
Maximum diameter, .... 
68 
59 
63 
Minimum diameter, .... 
55 
56 
61 
Index , ....... 
1. Distance from the opisthion to the 
80-88 
94-91 
96-82 
supra-orbital foramen, 
2. Distance from the supra-orbital 
182 
180 
189 
foramen to the alveolar point, . 
362 
333 
338 
Index ((2) = 100), 
50-27 
54-05 
55-91 
VOL. XXVII. 
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