190 THE GENERAL ANATOMY OF GORILLA [SECT. A 



that of the Gorilla, and has therefore gained an accession of some 

 500 gm. of additional cerebral material. 



2. In the adult Gorilla, the brain provides not more than 

 i_ part of the total weight of the animal, and may represent only 



_i__ part of that weight. The human brain provides about -^ of 

 the body-weight. 



3. The extent of the neo-pallium has been remarked already 

 as a distinctive character whereby the Primates may be ordinated. 

 The human brain possesses a vastly greater area of neo-pallium 

 than that of the Gorilla. The estimates of this excess seem to 

 vary somewhat. Thus one authority 1 states that in Man the neo- 

 pallium has six times the area found in the highest ape, whereas 

 data provided elsewhere 2 seem to indicate that the excess is repre- 

 sented by the figures 3'4 in the Chimpanzee, from which the 

 Gorilla is not very different. 



4. Taking a particular part of the neo-pallium, viz. the frontal 

 area (Brodmann 2 ) as a standard, it is claimed that this part pro- 

 vides 29% of the neo-pallial area in Man, while in the higher 

 Simiidae, the ratio is but 17% (in the Cercopithecidae about 40%, 

 in the Lemurs about 9%). 



The consideration of these statements leads to such reflexions 

 as the following : 



(a) In point of size or mass of the whole body, Man and the 

 Gorilla are sufficiently alike to exclude an appeal to the factor of 

 size as the influential element in determining such differences. 

 How important this may be in other cases, the study of small and 

 large mammals of the same group or order will soon convince an 

 investigator. It follows that the Gorilla's brain is to be regarded 

 as shewing the amount and the surface-area requisite for the 

 reception of the general sensory impulses arising from various 

 parts of the surface of an animal nearly equal to Man in bulk. 



(6) Another factor capable of determining an increase in the 

 size or area of some part of the brain has been mentioned also in 

 dealing with the lower forms. This is the particular development 

 of one or other of the special senses, that of vision being especially 



1 Elliot Smith, Rep. Brit. Ass. Dundee, 1912. Section H. President's Address. 



2 Brodmann, Anat. Anz. 1912, and Erganzungsheft, S. 211. 



