554 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 48. 



tion of the width of the skull to the basilar length, the variation 

 forms less than 6 per cent of the mean. It will be seen, too, that the 

 cranio-cephalic index shows relatively little variation. The greatest 

 and the least are found in two of the skulls in the American Museum 

 of Natural History. The variation in the length of the face, as shown 

 by the facio-cephalic index, is less than 3.5 per cent of the mean. 

 The position of the notch in the vomer is more subject to variation ; 

 in one case only is it nearer the foramen magnum than to the rear 

 of the hard palate. 



Salensky x has discussed the slight range of variation in the skull 

 of this species. 



Coming now to the zebras, the writer here presents measurements 

 and indices of eight adult skulls of Equus grevyi, of eight of Equus 

 quagga granti, of two of E. quagga chapmani, of three specimens of 

 E. quagga craws hay i, of one of E. quagga hohmi, and of one of 

 E. quagga cunninghami. All of these, now in the United States 

 National Museum, (except Crawshay's zebra, obtained by H. C. 

 Moore in central South Africa) were collected in British East Africa 

 by Theodore Eoosevelt, Kermit Eoosevelt, E. A. Mearns, Edward 

 Heller, and J. A. Loring. The first species considered is Equus 

 grevyi. 



Measurements of skulls of Equus grevyi in millimeters, with indices. 



Specimens in U. S. 

 National Museum. 



Basilar 

 length. 



Vertex 

 length. 



Frontal 

 width. 



Ce- 

 phalic 

 index. 



Cranial 

 length. 



Cranio- 

 cephalic 

 index. 



Facial 

 length. 



Facio- 

 cephalic 

 index. 



For. 



mag. to 

 vomer. 



Vomer 



to 

 palate. 



163228 $ 



545 



528 

 558 

 557 

 556 

 537 

 536 

 525 



615 

 590 

 615 

 627 

 632 

 600 

 600 

 595 



218 

 216 

 209 

 210 

 213 

 210 

 202 

 205 



40.0 

 40.5 

 37.4 

 37.7 

 38.3 

 39.1 

 37.6 

 39.0 



200 

 187 

 190 

 190 

 202 

 189 

 191 

 190. 



36.5 

 35.4 

 34.0 

 34.1 

 36.3 

 35.2 

 35.6 

 36.2 



422 

 413 

 428 

 443 

 437 

 415 

 410 

 408 



77.4 

 78.2 

 76.7 

 76.8 

 78.6 

 77.3 

 76.5 

 77.7 



130 

 132 

 134 

 130 

 131 

 136 

 128 

 122 



145 



182027 tf 



158 



182063 cf 



136 



163338 d 1 



140 



163331 $ 



141 



182028 ? 



132 



163334 $ 



142 



182026 $ 



135 







Averages 



543 



609 



210 



38.7 



192 



35.4 



422 



77.4 



130 



141 



There is observed here but little variation in the length and the 

 width of the eight skulls measured. The cephalic index varies 

 beyond the mean not as much as 5 per cent, and the difference be- 

 tween the extremes only 8 per cent. The index is very low, and this 

 horse is the most narrow-headed one known. The facio-cephalic 

 index neither rises above nor falls below the mean more than 1.5 

 per cent. The cranio-cephalic index is very stable, and the facio- 

 cephalic still more so. The vomerine notch is usually nearer the 

 foramen magnum, as in the domestic ass. 



1 The Przevalsky Horse, Bradley and Hayes Translation, p. 28. 



