130 EINAR LONNRERG, MAMMALS COLLECTED BY THE SWEDISH ZOOLOGICAL EXPEDITION ETC. 
A Horse with such a dentition would be between 3/2 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 Grévy’s Zebra as in a Horse. The same 
appears also to hold good for Béhm’s Zebra as the dentition of such a skull in a 
somewhat earlier stage is as follows: 
Upper jaw: 1;.d1°, di*, ‘de, pt p.. dp. (p)> mm. mm. (nee): 
Lower jaw: i, di, (is), dis, de, po, Ps. Apy, M,,-Ms, (m5). 
There is a rather striking difference of type between the skulls of the Grévy’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 F#. 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 Grévy’s stallion (conf. table of measurements above). The 
greatest breadth of the skull is with other words only 36 °/o of the condyloincisive 
length in #. grevyi but 42°/, in EB. b. antiquorum. The least interorbital breadth of 
the latter is 156, that of the former 143 mm. thus resp. 29 and 24 °/o of the condy- 
loincisive length of skull. The difference in length between the skulls of HL. grevyi 
and #. 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 H#. grevyi stallion 186 mm. but in the FL. 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 EF. 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 ZH. grevyi is 
138 mm., and the width at the base of i® is in H. 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 2. burchelli series are considerably smaller 
than EF. 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 Grévy’s Zebra. Thus the greatest breadth of FE. b. granti is 39 °/o (perhaps some- 
times 40), and the least postorbital width 27 °o of the condyloincisive length of the 
skull. 
‘ On one side p* just cutting the gum. 
