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



like processes growing from the frontal bone on each side and meeting in the 

 middle line. In this disposition we encounter a rare occurrence, viz. the 

 encroachment of the membrane-bones of the skull upon the territory of this 

 basis cranii. The principal points of importance in the mandible are its very 

 massive character in proportion to the rest of the skull ; the ascending ramus, 

 which is higher than in Hylobates, and which bears a shallow sigmoid notch. 

 But in fact the mandible is found to present several distinct variations. Thus 

 the relative height of the ascending ramus is by no means constant : the 

 lower margin of the body of the jaw may be rectilinear, sinuous, or uniformly 

 curved. Consequently some of the mandibular types described as distinctive 

 of certain varieties of Man may be shewn to possess counterparts in the jaw 

 of the Orang-utan. 



The teeth provide the normal formula, but in males accessory molar teeth 

 are extremely common. The great length of the roots of all the teeth is 

 noticed by Tomes {Dental Anatomy) as peculiar : also the curious crenation 

 of the enamel (which, though a feature of the developing tooth, persists in the 

 crowns of the molars of the Orang-utan) is remarkable. The third molar 

 tooth in the upper jaw tends to smaller dimensions than the other two. 



CRANIAL CHARACTERS OF ANTHROPOPITHECUS NIGER. 



There remain to be enumerated the cranial characters of the 

 Chimpanzee (Anthropopithecus niger). It may be pointed out 

 that this ape and the Gorilla agree in several important respects 

 wherein they both differ from the Orang-utan. This general 

 statement applies to the skull as well as to other anatomical 

 structures. 



Taking as our example a young, but nearly mature, individual 

 (Fig. 146), we notice that, viewed from above, the skull of the 

 Chimpanzee is more ovoid in form than that of the Orang-utan. 

 The facial skeleton is rather smaller in proportion to the cranial 

 part than in either the Orang-utan or the Gorilla, and here in the 

 Chimpanzee skull (especially in infancy, cf. Fig. 147) suggests the 

 proportions of the human skull, though it is still far from realizing 

 them. 



The cranial capacity of adult males provides an average value of about 

 400 c.c. (Oppenheim, op. cit. p. 138 gives 404*3 c.c.) with a maximum of 

 470 c.c. The adult female skull is less capacious and amounts to about 

 95 7 °f that for the male. The instructive table drawn up by Oppenheim 

 is reproduced here in order to exhibit the sexual variability in several of the 



