150 ARBOREAL MAN 



and primitive Mammal which constitutes the ideal 

 ancestor the ancestor which possessed the ideal Proto- 

 mammalian brain. 



Although the brains of all existing Reptiles are too 

 highly specialized, in one direction or another, in harmony 

 with the specialized lives of their possessors, still it is 

 to them, and to the much more lowly Dipnoi, that we 

 must turn to obtain any concrete picture of the brain 



PIG. 59. DIAGRAMMATIC OUTLINE OF A PRIMITIVE TYPE OF 

 VERTEBRATE BRAIN. 



C.H., Cerebral hemisphere, practically all of which is devoted 

 to the sense of smell = archepallium. A small area, repre- 

 sented by coarseTTlots, indicates a portion of the cortex 

 connected with non-olfactory impressions. 



of the earliest Mammal. The anatomical features need 

 not be discussed in detail. Upon broad lines, such a 

 brain consists of a collection of ganglionic masses, each 

 mass definitely allotted to a particular sense or a particular 

 function. To such a brain, impressions from special 

 sense organs come by definite channels each to its definite 

 anatomical station within the brain, and these central 

 ganglionic stations are in free communication with each 

 other. In addition to all this there is, as an outgrowth 

 from each side of the brain, a small cerebral hemisphere, 

 forerunner of the great cerebral cortex of the higher 

 types (see Fig. 59). It is in these cerebral hemispheres 

 that all the possibilities of evolution lie. It is the func- 

 tion of the cortex that it provides an organ in which are 

 blended the impressions that come by the several channels 



