130 BINAR LONNEERG, MAMMALS COLLECTED BY THE SWEDISH ZOOLOGICAL EXPEDITION ETC. 



A Horse with such a dentition would be between 3 Va and 4 years. It is possi- 

 ble that this specimen is not quite as old, but the relative order for the succession 

 of the teeth appear to be the same in Grevy's Zebra as in a Horse. The same 

 appears also to hold good for Bohm's Zebra as the dentition of such a skull in a 

 somewhat earlier stage is as follows : 



Upper jaw: i\ di^ di*, do, p^ p% dp*, (p*)S m\ m^ (m"). 

 Lower jaw: i, dig (i2), dig, dc, pg, ps, dp^, m^, mg. (^3)- 



There is a rather striking difference of type between the skulls of the Grevy's 

 Zebras (PL VIII Figs 1, 2 & 3) and those of the burchelli series from South Africa. 

 The former have a much longer and comparatively more slender skull, while that 

 of the latter is comparatively short and broad. The condyloincisive length of a 

 skull of an old male E. b. antiquorum. is for instance only about 530 mm., but its 

 greatest breadth is fully 223 mm., thus more than the corresponding measurement 

 of the longer skull of the Grevy's stallion (conf. table of measurements above). The 

 greatest breadth of the skull is with other words only 36 "/o o^ the condyloincisive 

 length in E. grevyi but 42 "/o in E. b. antiquorum. The least interorbital breadth of 

 the latter is 156, that of the former 143 mm. thus resp. 29 and 24 7o of the condy- 

 loincisive length of skull. The difference in length between the skulls of E. grevyi 

 and E. b. antiquorum is chiefly due to the prolongation of the facial portion of the 

 former, for the distance from the anterior brim of the orbit to the posterior surface 

 of the occipital condyle is practically the same in both. On the other hand the 

 distance from the anterior brim of the orbit to the tip of the premaxillaries is 

 resp. 365 and 336 mm. In correspondence herewith the length of the palate mesially 

 is resp. 372 and 352 mm. The different length of the molar series is also very strik- 

 ing. It measures in the E. grevyi stallion 186 mm. but in the E. burchelli anti- 

 quorum 151 mm. In spite of its length the facial portion of the skull of E. grevyi 

 is comparatively more slender as well in breadth as in height. The width of the 

 skull just in front of the orbit is in E. grevyi 185 mm., but in E. b. antiquorum 197 

 mm. The latter skull is, however, more suddenly narrowed so that it measures 132 

 mm. across the anterior margin of m* while the same measurement of E. grevyi is 

 138 mm., and the width at the base of i* is in E. b. antiquorum, 63 and in E. grevyi 

 71 mm. The height of the skull expressed by measuring the distance between sutura 

 nasalis and the alveolar margin of p* is 137 mm. in the former and only 131 mm. 

 in E. grevyi. 



The East African members of the E. burchelli series are considerably smaller 

 than E. b. antiquorum. Their skulls are neither so broad, nor so heavy as those of 

 their southern relatives. They are, however, comparatively broader than the skull 

 of Grevy's Zebra. Thus the greatest breadth of E. b. granti is 39 7o (perhaps some- 

 times 40), and the least postorbital width 27 7o of the condyloincisive length of the 

 skull. 



1 On one side p'' just cutting the gum. 



