CHAP. V] THE CRANIA OF THE SIMIIDAE (PRIMATES) 



225 



following. The characteristic prognathism of the ape is very 

 marked. The constituent elements of the nasal septum corre- 

 spond individually to those seen in a similar section of a human 

 skull, the differences consisting in the details of contour and con- 

 formation. In relation with the greater size of the maxilla the 

 system of air-spaces is more extensive in the simian skull ; this is 

 best seen when the nasal septum is removed (or when that side of 

 the skull which does not include the septum is examined). The 

 air-spaces are produced by an "invading" tissue, to wit the mucous 

 membrane lining the nasal fossae. The extraordinary power of ab- 

 sorbing osseous tissue possessed by the cells of this tissue is not 



Fig. 150. The sphenoethmoidal, spheno-maxillary, and foramino-basal angles 

 are shewn in the crania of (A) a New Britain native (male) ; (B) a Gorilla (male) ; 

 (C) a Dog. n, pr, b, Spheno-ethmoidal angle; p, pr, b, spheno-maxillary angle; 

 pr, b, op, foramino-basal angle. 



devoid of significance, when their origin from ectodermal cells is 

 recalled to mind. However produced, the air-spaces confer an 

 obvious advantage, viz. that the weight of the skull is reduced 

 without sacrifice of strength, and also without loss of surface for 

 the attachment of muscle-fibres. 



The ape is seen to possess extensive sinuses in the sphenoid, 

 ethmoid and maxillary bones, but not always in the frontal 

 bone, a point wherein the Orang-utan differs from the African 

 Simiidae (Chimpanzee and Gorilla), which are here more closely 

 allied to man than is the first-named form. If the maxillary 

 antrum in the skull of a Gorilla be exposed on the facial aspect 

 of the jaw, a large bullous dilatation of the nasal duct will be 



n. m. 15 



