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



stress upon the differences observed in the profile of the face in 

 various examples. Thus it was noticed that some crania preseni 

 a straight facial outline, the flattening of the nose having been 

 carried to this extreme. But a second type surpasses even the 

 former in this respect, for the profile is so to speak " concave " or 

 hollowed-out as Fitzinger describes it. The accompanying illus- 

 tration (Fig. 145) shews a cranium with a moderately hollowed-out 

 profile. To this type, the epithet simognathic was given by 

 Selenka, and more recently (1913) Keith applied the term simo- 

 prosopic to the same condition, regarding it as generally distinctive 

 of the Orang-utan in contrast with the other Simiidae. Keith's 

 contribution to this subject is of great importance, for he shews 

 that in respect of its facial conformation, the Orang-utan has 

 experienced a change analogous to, if not identical with, that 

 distinguishing the bull-dog from the more normal canine varieties. 

 And further, it is claimed that the defective growth of bone may 

 induce a similar condition in the human skull, in which it has 

 been long known as Achondroplasia. Several other illustrations 

 will be added in the sequel. Here it will suffice to note that 

 even though not all crania of Orang-utans are strictly simognathic, 

 yet all tend to this condition, which is so distinctive as to provide 

 a most ready means of identifying the crania of this genus of the 

 Simiidae. 



Taking for descriptive purposes a young individual on the verge of 

 maturity we remark at once the great increase in size upon that of the 

 Hylobates skulls. The proportions too of face and cranium are different, the 

 facial part having gained in bulk ; to this gain a notable contribution is made 

 by the mandible. 



In proportions, the cranial part of the skull is, when contrasted with 

 the facial part, less elongated than in Hylobates, and presents the nearest 

 approach to brachycephalic proportions (cf. Chapter xi) met with among the 

 Simiidae. The cranial capacity ranges from 355 c.c. to 540 c.c. in adult 

 males, and from 300 c.c. to 490 c.c. in females (Hrdlicka) 1 . The cranial 

 sutures early become simplified and are closed by synostosis. Traces of the 

 division of the parietal bone into upper and lower halves are stated by Banke 

 to be very frequent (the trace consisting in a remnant of the dividing suture 

 persistent at its starting point from the coronal suture). 



Rapidly converging from the external angular processes of the frontal bone, 

 the temporal ridges vary in their ultimate conformation, the sexual factor being 



1 Proc. United States National Museum, Vol. xxxi. p. 544. 



