342 STRUCTURE AND ADAPTATION OF TEETH 



hair), down to our own times, altliougli accurately 

 scientific accounts of tlie animal have not until 

 very recently been obtained. The canines of the 

 gorilla are larger and more projecting than in the 

 chimpanzee, and the upper molar series are even 

 inclined somewhat outward, in a direction oppo- 

 site to that of the arch of the human jaw. 



In the adult orang and chimpanzee the massive 

 jaws are acted upon by muscles which attain a 

 very powerful development, indicated by the wide 

 zygoma and the deeply depressed surface of the 

 skull for the insertion of the large temporal muscle. 

 The sagittal and lambdoidal crests are very high; 

 but these characteristics are still more marked 

 in the gorilla, and the immense projecting supra- 

 orbital ridge bestows a singularly distinctive 

 feature upon the animal's expression. The pro- 

 minence of the crests, and the great development 

 of the muscles, tend greatly to increase the appa- 

 rent size of the skull; but the organs of the senses 

 still bear a very large proportion to the brain cavity, 

 and the faculties of sight, hearing, and smell are 

 remarkably keen. 



The immature skulls of the chimpanzee and 

 orang, which I here present to your notice, supply 

 a highly interesting opportunity for comparison 

 with the adult skulls. It will be observed that 

 the capacity of the cranium in the young orang, 

 at the age when the first permanent molar is 

 acquired, very nearly equals that of the cranium 



