NERVE 179 



of which is speciall}^ associated with the higher mental 

 activities (fig. 90). 



Further, in the group of mammals which depend largely 

 on olfactory impressions, the rhinencephalon is markedly 

 developed, while in those in which smell plays a sub- 

 ordinate part this portion of the brain is only slightly 

 developed (fig. 61). 



It must at once be recognised that if such special parts 

 exist, each must he in nature receiving, reacting, and, to 

 some extent, associative. Thus, if one part of the cortex is 

 specially connected with the reception of impulses from the 

 eye, it must be able to bring about appropriate reactions 

 either by sending impulses directly outwards or by acting 

 upon some part of the brain which has the function of 

 bringing about a reaction. And, in order that the reaction 

 may be appropriate, some associative mechanism, either in 

 these parts of the cortex or elsewhere, must be brought into 

 play (fig. 89). 



V. THE INTEGRATION OF SENSATIONS IN 

 THE CORTEX. 



The Cortex Cerebri and Mental Life- 



We have seen that stimulation of definite parts of the 

 €ortex cerebri may lead not only to modification of move- 

 ment through the spinal arcs, but also to changes of 

 consciousness, which have been described as sensations. 



But the great object of the development of the cerebral 

 ■cortex from the basal ganglia is to furnish a means 

 by which these sensations are associated and integrated, so 

 that more complex changes of consciousness may result. 

 A full study of this is beyond the domain of physiology and 

 •encroaches on the territory of the psychologist. 



A pine tree may, through the visual mechanism, produce 

 a sensation of green of a certain extent and from a certain 

 direction ; the odour niay act upon our olfactory 

 mechanism ; the wind in the branches may stimulate our 

 hearing, and when we approach and touch the tree our 



