IMPRESSIONS OF SIGHT AND HEARING 179 



field in its turn is pushed backwards by the expansion of 

 the neopallium, and so comes to occupy the posterior limit 

 of the cerebral hemisphere; and it, in its turn, becomes 

 separated from the sensory area by an intervening area 

 of cortex. An altogether new field, the prefrontal or 

 silent area, is developed at the anterior extremity of the 

 hemisphere, and it, by its growth and expansion, is largely 

 instrumental in bringing about the rotation around the 

 island of Reil, which has been described. In the brain 

 of a Lemur, and more markedly in the brain of a Monkey, 

 the original neopallial areas allotted to the several senses 

 have (1) migrated from before backwards round the 

 island of Reil as a centre, (2) have tended by their growth 

 to submerge this fixed field of cortex, and (3) have become 

 separated from each other by ever-widening fields of 

 intervening cortex (see Figs. 67 and 68). It is these 

 intervening areas, known as " association areas," which 

 are of interest. In them there is every reason to believe 

 that the impressions represented in the bounding areas 

 are blended and co-ordinated. It is these association 

 areas between the auditory and the visual, and between 

 the visual and the sensory fields which, enlarging in 

 the arboreal Primates, become the distinctive feature of 

 the human brain (see Fig. 69). And this anatomical 

 condition is the result we should expect from studying 

 the educational possibilities of the arboreal life. 



