CHAP. IV] THE GENERAL ANATOMY OF GORILLA 



173 



sometimes a fifth incisor (of large size and so probably not a retained milk 

 tooth) is seen in the mandible. Further details as to the dentition are 

 provided and commented upon in Chapter vi. 



The mandible is of enormous size and weight. The rami diverge but 

 slightly and the post-canine teeth are set in two nearly parallel series. No 

 prominence is seen in the symphysial region, the chin being absent or 

 retreating. The genial tubercles are not distinct, for they are usually repre- 

 sented by a vertical ridge much nearer the lower border of the symphysis 



C D 



Fig. 116. The left auditory meatus and its surroundings in A, Orang-utan; 

 B, Gorilla; C, Chimpanzee; and D, Man (Swat river tribesman). The parts to 

 be noticed specially are: i. the tympanic bone which is below the meatus, and has 

 a different form in each case; ii. the conoid process, which is in front of the 

 meatus, and much smaller in Man than in the Apes; iii. the mastoid process, 

 which is behind the meatus, and in the Gorilla is not unlike that of Man. 

 (W. L. H. D. del. from specimens in the Cambridge Collection.) 



than the corresponding tubercles in Man. The anterior belly of the M. di- 

 gastricus makes little or no impression on the bone, the mylo-hyoid ridge is 

 absent, and the mylo-hyoid groove, though recognizable, is shallow save where 

 it commences beneath the flange-like lingula. The ascending ramus is very 

 high, and the sigmoid notch shallow, but the coronoid process extends above 

 the level of the condyle. Altogether this region of the mandible offers a 

 special contrast with the human jaw. The condylar neck is short and the 

 condyle flattened. This character bears some relation to the form of the 

 glenoid fossa, which is, as above described, shallow. The shallowness might 

 be held to indicate free lateral movements of the mandible in mastication. 



