56 



ANTHROPOID APES. 



it will be well to note the important differences 

 between the structure of the skull of a young and 

 aged male, and of a young and aged female gorilla. 

 The skull of the aged male animal is large and 

 heavy. Its average weight is one and a quarter 

 kilogrammes. The longitudinal diameter, from the 



Fig. 15.- Skull of an aged male gorilla in profile. 



alveolar point of the upper jaw to the occipital 

 point, may be as much as 294 mm. The over- 

 hanging orbits are high in front, and flattened off 

 behind, and their upper edges unite to form a ridge 

 in the middle of the face. To these the back parts 

 of the orbits are attached, in shape like a trun- 

 cated cone, round and prominent in front, and nar- 

 rowing into bony capsules in the direction of the 

 brain-pan. They open directly in front, and the 

 aperture is generally in the form of a regular square. 

 The edg^s are seldom so blunted off as to present a 

 figure somewhat approaching to a circle (com p. 



