174 THE GENERAL ANATOMY OF GORILLA [SECT. A 



Such a conclusion would be erroneous, for the fact that the canine teeth 

 surpass those adjacent to them in height, favours a simple hinge-like 

 movement of the temporo-mandibular joint. This is an important distinction 

 from the human arrangement (and the accuracy of the conclusion is con- 

 firmed by the small size of the external pterygoid plates). Such movements 

 of the mandible react on the mode of abrasion of the dental crowns 1 , a 

 matter to be discussed in the sequel. 



These notes refer more particularly to the skull of a young male indi- 

 vidual. The adult male differs in certain features which have been indicated 

 above. In female skulls, the permanent characters resemble those set forth 

 in detail here, since the intensive development of the distinctive male features 

 never occurs. On the other hand, very immature examples also present dis- 

 tinctive characters, and on the whole they may be considered to approximate 

 more nearly to the human cranial type. In fact the gorilla-type diverges 

 from that of Man at an early period, the contrast becoming more marked 

 with the increase in age. 



(6) The Vertebral Column. In the cervical region of the 

 vertebral column the enormous length of the vertebral spines is 

 the most striking feature : these spinous processes are not however 

 bifid, and thus differ from those of the existing human races of 

 Europe although approached in this respect by the cervical 

 vertebrae of some of the primitive human races in other regions, 

 and also the prehistoric skeleton from La Chapelle aux Saints in 

 France. The costal process is sometimes imperfect, so that there 

 is no canal between it and the true transverse process. The costal 

 process of the sixth cervical vertebra is large, while that of the 

 seventh is very small, the same proportions obtaining as in Man. 



In the thoracic region thirteen vertebrae are common, though 

 occasionally fourteen rib-bearing vertebrae occur. Their centra 

 appear as though laterally compressed (in comparison with those 

 of Man) : the transverse processes are stunted but massive : the 

 spinous processes of the lower members of this series tend to 

 be bifurcated. The section of the thorax in the horizontal plane 

 differs from that of Man in the relatively larger proportion borne 

 by the antero-posterior to the transverse diameter. The thorax 

 is thus intermediate between the human type, and the pithecoid 

 form as shewn by Cercopithecidae. 



The usual number of lumbar vertebrae is three (Fig. 118), 

 although four vertebrae are of frequent occurrence. 



1 Cf. Keith, Proc. Roy. Soc. Medicine, Odont. Section, 1913, p. 16 of reprint. 



