CHAP. XXIV.] PRINCIPAL PARTS OF THE BRAIN. 485 



(or the Sensorial and what some regard as the Volitional) 

 which are immediately brought into relation by means of 

 the Corpus Callosum. But even if this supposed arrange- 

 ment be the one that actually exists, it would by no means 

 indicate that the organic seats of the more complex deriva- 

 tive processes are not also mediately brought into relation 

 with one another. The more specialized Emotional, Intel- 

 lectual, and Volitional Regions in each hemisphere, wher- 

 ever they may be, and however they may be related to 

 one another, are necessarily, by means of the ' association 

 system ' of fibres, brought into intimate communion with 

 their corresponding Sensorial Regions of various lands, it 

 is in this indirect way, therefore, that the higher functional 

 regions of the two Hemispheres may be brought into rela- 

 tion with one another, through the medium of the fibres of 

 the Corpus Callosum. There is manifestly a unity in our 

 Emotional, Intellectual, and Volitional as well as in our 

 Sensorial Consciousness that is, in the ' derivative ' as 

 well as in the ' primary ' mental processes. 



There can be little doubt that Sensorial Activity and 

 the action of those portions of the Brain which are directly 

 concerned therewith, affords the primary or essential basis 

 of Consciousness. We are most fully conscious when 

 we are most receptive of external impressions, and we 

 lapse into a completely or partially unconscious condition 

 when the advent of such impressions is for a time 

 prevented, or when we are intensely absorbed in some 

 train of thought (Ideal or Reflective Consciousness) that 

 is, when the activity of other portions of the Cerebral 

 Hemispheres in some way dwarfs or eclipses that of the 

 sensorial regions proper. An admirable illustration of the 

 former truth has been lately given by Dr. Striimpell,* 



* " Pfliiger's ArcMv," vol. xv. p. 573, and translated in "Nature,"' 

 December 13, 1877. 



