l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6l 



but it needs only an examination of such a set of zebra skulls as have 

 been gathered at the U. S. National Museum to convince one that 

 there exists in probably every species of Equus great individual 

 variations in the regions under consideration. 



In the Liakhof horse the width of the skull at the articulation for 

 the lower jaw is 14 mm. greater than in the Alaska skull. The width 

 across the hinder ends of the nasals, taken in a straight line, is 118 

 mm. in the Alaska skull ; in the Liakhof skull it is given as 126? The 

 orbit in the Alaska skull is smaller than that of the other, the hori- 

 zontal measurements being respectively 66 mm. and 67 mm. ; the 

 perpendicular, 55 and 61. The face of the Alaska horse appears to 

 have less height than that of the Liakhof horse, the height measured 

 at the rear of the last premolar, being in the former, 132 ; in the latter, 

 140 mm. The nose of the Alaska skull appears to have been, some- 

 what longer (from front of the premaxillae to the front of pm. 2 ) 

 than in the other skull, being 134 mm. as compared with 129 mm., a 

 relatively small difference. The length of the diastema between i. 3 

 and pm. 2 is the same in both. Tscherski notes, in the skull discov- 

 ered by him, a concavity which occupied a considerable area just 

 above the maxillary ridge. In the Alaska skull there is a corre- 

 sponding cavity somewhat larger and deeper. In some specimens 

 of Grant's zebra this region is strongly convex ; in others, it is 

 slightly concave. It is possible, of course, that a character variable 

 in one species will be constant in another. The face of the Liakhof 

 skull is somewhat wider on the maxillary ridge than in the Alaska 

 skull, being 191 mm. as compared with 182 mm. These maxillary 

 ridges extend farther forward in the Alaska skull than in the other, 

 reaching nearly to the middle of the hinder premolar ; in the Liakhof 

 skull, to about the middle of the first molar. 



The hard palate of the skull last named ends in the midline oppo- 

 site the middle of m. 3 ; in the Alaska skull it ends opposite the hinder 

 end of the protocone of m. 2 The distance from the front of the 

 foramen magnum to the hinder edge of the hard palate is almost 

 exactly the same in the two skulls. From the front of the foramen 

 to the edge of the vomer, at the midline, the distance is 131 mm. in 

 the Liakhof skull; in the Alaska skull, 121 mm. From the same 

 point of the vomer to the edge of the hard palate is 109 mm. in the 

 Liakhof skull ; in that from Alaska, 1 14 mm. In the last-named skull 

 the index obtained by dividing the smaller distance multiplied by 

 100, by the greater is 83.2 ; in the former skull, 94.2. It remains to 

 be proved that this difference is of specific value. Tscherski stated 

 that the incisive foramina, or fissures, in the skull which he described 



