160 



THE GENERAL ANATOMY OF GORILLA 



[SECT. A 



with the smaller Hylobates, shews that the Asiatic Simiidae follow 

 the same rule 1 .) 



The thorax is of great width and depth though relatively 

 short ; hence the trunk is stout and this appearance is enhanced 

 by the protruding paunch of well-nourished individuals. The 

 stomach is of enormous size in an adult male specimen (Mus. 

 Anat. Cant. Cy), and capable of containing many pounds by weight 

 of the vegetable food on which these animals chiefly subsist. 



The external genitalia are remarkable for their small size even 

 in adult male individuals. Ischial callosities are absent (as in all 

 the Simiidae save Hylobates). Since the staple diet of the Gorilla 

 is neither scarce nor difficult to obtain, an explanation of the 



Fig. 101. Head of adult male Gorilla. 

 (Holt Don., Mus. Anat. Cant.) 



Fig. 102. Head of adult female 

 Chimpanzee. (Mus. Anat. Cant.) 



colossal strength of this anthropoid ape must be sought in another 

 connexion. On the whole it seems probably indicative of the 

 need for protection from enemies newly encountered when arboreal 

 life is first or partly abandoned. These peculiarities of the Gorilla 

 suggest therefore that we are dealing with a form which has been 

 enabled to survive by the fulfilment of that condition. The 

 general structure leads to the conclusion that the ancestors of 

 the Gorilla were more definitely arboreal than their descendants. 

 Certain contrivances seem to be indispensable by way of providing 

 for the erect attitude, when the " raw material," so to speak, is 

 " primate." The Gorilla has progressed further than any other of 



1 Cf. Pocock, P.Z.S., 1905, Vol. n. p. 179. 



