290 



DE. E. EAY LANKESTEE ON OKAPIA. 



the bones of the skull show a very considerable system of sinuses separating the upper 

 and under surfaces of certain regions of what are usually flat bones (see text-fig. 5, p. 28G j. 

 This "tumescence" of cranial bones occurs in various Uugulata and other mammals; 

 but it is not developed in other Pecora in the same regions and to the same extent as 

 it is in Olapia and Gimffa. In 01caj)ia it is largely developed in the orbital region of 

 the frontal bone (text-fig. 10), and in the adjacent parietals in Giraffa (toxt-fig. 11, 

 p. 291). Also in botli genera tumescence occurs in the expanded nasal region 



Text-fi". 10. 



Yiew from above of the fronto-parietal region of the skull (larger of the two specimens) of the Okapi. 

 occ.li; angle of the occipital crest ; g.t.l., position of the lateral tumescence forming the paired parietal horns 

 of the Giraffe, absent here ; ot.l., the lateral frontal tumescence of the Okapi, absent in Giraffe ; z>j., the 

 zygomatic arch ; po., posterior angle of the orbit ; ao., anterior angle of the orbit ; pLv., pralacrymal 

 vacuity; otm., the slight median tumescence of the base of the nasals of the Okapi ; sof., supraorbital 

 fossa : afp., the fronto-parietal suture. 



For comparison with text-figure 11. 



either in the nasals themselves or in the adjacent region of the frontals. The strong 

 development of the supraoccipital crest in both skulls (text-figs. 2 & 3, p. 284) is not 

 precisely of the same nature, for the thickened bone is not there excavated by sinuses. 

 I shall revert to this matter immediately, but must here point out the remarkable 

 form and aspect of the orbit of the Okapi, which is connected with the tumescence 

 of the bone which forms it. The orbit is rectangular, not circular as it is in 



