10 



GORILLAS AND CHIMPANZEES 



By a careful study of the voices together with the 

 skulls of animals, it is found that the gnathic index 

 can be relied upon as a vocal index. The ape has 

 the smallest angle between the spinal axis and the 

 facial plane, and has the greatest vocal range and 

 purest voice of any other animal below man. 

 Among the apes the gibbon has the smallest angle, 

 and he also has the best vocal qualities of any other 

 ape. 



The contour of the skull in all parts conforms to 

 the angle of its projection from the spinal axis. It 

 is depressed and elongated in proportion as the 

 angle increases : the brain cavity is narrowed in a 

 like proportion to its length, and the brain, of course, 

 is modified in the same manner. 



The brain of the ape resembles that organ in 

 man as closely as his skeleton resembles man's. It 

 has the same lobes, convolutions, and centres. The 

 texture is slightly coarser. The small details are 

 less intricate and their lines somewhat less distinct. 

 But these also differ to a certain extent in different 

 men. In man and apes the same nerves are present 

 and connect the same organs of sensation, volition 

 and motion. In all essential points they are one. 



These leading facts are deemed sufficient to show 

 the physical likeness of apes to man, and we shall 

 refrain from the minute details that would only be 

 of interest to the specialist. The purpose is to 

 acquaint the general reader with the leading facts. 



Regarding man purely in the light of an animal, 

 it is evident that he is, physically, very closely allied 



