Explanation of PLATES 13-17. 



PLATES 13-17. 



The figures in Plates 18 — 17 show the dorsal views of fifteen skulls of the Okapi in 

 the British Museum, the Museums of Edinburgh, Tervueren, Rome, Madrid, Genoa, and 

 Paris, and the private collections of Major Powell-Cotton and the Hon. Walter Rothschild, 

 drawn mainly from photographs taken with a telephoto lens, with the basicranial axis of 

 the skull set normally to the line drawn from the centre of the skull to the centre of 

 the lens. 



With a view to facilitating a comparison of the length of the nasal region of the 

 various skulls with the postorbital breadth, for the purpose of deciding whether two 

 types of skull, "broad" and "narrow," can be distinguished, dotted lines have been 

 drawn in the figures to explain the method of obtaining the ratios mentioned in the 

 legends beneath the figures. The distance MN is the distance from the front of the 

 suture between the nasal and premaxillary bones to the outer end of the suture between 

 the nasal and frontal bones, that is, to the foremost point of the frontal bone. This 

 distance gives a fair indication of the length of the facial parts of the skull. The distance 

 from the front of the premaxillary bones would possibly have been a better criterion, but 

 the selection of the above measurement was largely determined by the absence of the 

 premaxilla? in some of the skulls. The distance EE is the maximum width of the skull 

 in the region of the postorbital arch. This gives a fair indication of the breadth of the 

 skull as a whole. The ratio EE (or MM) to MN gives roughly the breadth of the skull 

 in terms of the length of the facial parts. Thus, in skull C the ratio EE (or MM) to MN 

 is 198-9 : 100, in skull B it is 179-3 : 100; so that C is a relatively broader skull than B. 



The fifteen Okapi skulls specially studied are for convenience denoted by the letters 

 A — P. The particulars of these, so far as concerns the illustrations published in this 

 Atlas, are as follows : — 



Plate 13. 



Skull A. — In the British Museum; Reg. No., 1.8.9.51; presented by Sir Harry 

 Johnston in 1901. Sex doubtful: when first described supposed to be female because 

 of absence of ossicones, soft rudiments of which were, however, present ; young, about two 

 thirds grown. Locality : Semliki Forest, near Lake Albert Edward. The skull is 

 figured by E. Ray Lankester, 'Trans. Zool. Soc.,' 1902, vol. xvi, plates xxxi and xxxii, 

 and pp. 284 and 290. Figured also in Plates 3 and 8 of this Atlas. This skull, with 

 the corresponding skin (see Plate 44, fig. 1), is the type of Okajda erikssoni, Lankester 

 ('Ann. Mag. Nat. Hist.,' ser. 7, x, 59, November, 1902, p. 417). 



Skull B. — In the British Museum; Reg. No., G. 12.27.1 ; part of a complete skeleton 



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