220 THE CRANIA OF THE SIMIIDAE (PRIMATES) [SECT. A 



of the suture dividing the parietal bone from the squamous portion of the 

 temporal bone is to be noted. 



Bony crests occur on the surface of the cranium, but are comparable 

 rather to those of the Orang-utan than to those of the Gorilla. For it is 

 the exception rather than the rule for the temporal ridges to form a 

 median sagittal crest : they commonly run in close approximation along 

 the sagittal suture, diverging thence with the formation of lateral lambdoid 

 crests. 



The contour of the orbit is less definitely elliptical than in the Orang-utan, 

 and herein the Chimpanzee and Gorilla resemble one another ; similar agree- 

 ment between the two African apes is seen in the prominence of the external 

 angular processes of the frontal bone, in the continuity of the supra-orbital 

 ridge between these two processes and across the inter-orbital space, in the 

 bevelling of the external orbital margin, and in the shortness of the lachrymo- 

 ethmoidal suture. The lachrymal hamulus is vestigial, and the spheno- 

 maxillary fissure reduced to a narrow cleft. 



The nasal aperture is pyriform, with the truncated apex above ; the lower- 

 margins of the aperture are obliterated, and no nasal spine is seen. The nasal 

 bones are often conjoined at an early epoch, and their flat expanse is not 

 relieved by the very remarkable median ridge so characteristic of these bones 

 in the Gorilla. The nasal bones preserve a more uniform breadth from above 

 downwards than in the Gorilla, and do not extend so far below the level of 

 the lower orbital margins as in the latter animal. 



In the development of frontal air-sinuses, and of similar air-cavities in the 

 ethmoid bone, with dilation of the nasal duct, where this is in relation with 

 the maxillary antrum, the Chimpanzee and Gorilla agree, and approximate to 

 the human condition (cf. Keith, Proc. Anat. Soc, 1902), while they differ 

 herein from the Orang-uta.n and Gibbon. 



The maxillary antrum is of smaller extent, both absolutely and relatively, 

 in the Chimpanzee than in the Gorilla. The reduction affects all parts of 

 the antrum, but sometimes the upper and hinder portion is particularly 

 diminished. In such instances I have noticed that the foramen rotundum 

 is visible when the orbital cavity is viewed from in front. But this is by no 

 means always the case in the Chimpanzee. I may add that the foramen 

 rotundum is thus visible usually in the Cebidae, and occasionally in the 

 Cercopithecidae. Once only have I seen this condition in a human skull, 

 viz. that of an African negro dissected in the Cambridge Anatomy School. 

 But inflation of the antrum is by no means the only factor involved in this 

 matter, which cannot be pursued further in this place. The palate has the 

 characteristic simian hypsiloid contour, and the post-palatine spine is small, 

 as is also the tuber maxillare. The maxillary antrum is said to extend into 

 the palatine portions of the maxillae. Great irregularity of the arrangement 

 of the palatine sutures is frequent. 



The temporal fossa owes its depth largely to the channelling of the 

 alisphcnoid, which commonly articulates with the frontal and squamosal 



