Chap. XXIV.] PRINCIPAL PARTS OF THE BRAIN. 483 



2.— The Functional Relations of the Cerebral Hemi- 

 spheres with one another: the Duality of Body 

 and the Unity of Mind. 



The two Cerebral Hemispheres are now generally 

 admitted to contain the ultimate prolongations of the 

 * ingoing ' nerves, or nerves of Sense, and to be constituted 

 by the aggregation of the organic centres (abundantly 

 interconnected by ' commissural' fibres) of all those higher 

 mental processes which we have traced as derivatives of 

 the exercise of conscious Sensibility, viz., the specially 

 automatic processes of Perception, Ideation, Emotion, 

 Conception, Reasoning, together with the more volitional 

 processes of Attention, Recollection, Imagination, and 

 Constructive Thought. The. Cerebral Hemispheres con- 

 tain, however, in addition to the Sensory Centres and 

 those for the derivative processes above indicated, multi- 

 tudes of fibres and some Centres for the conduction and 

 proper grouping of * outgoing ' currents. 



Of the various transverse commissures, already described, 

 that connect these parts with one another, one, of more 

 importance than the others, now deserves some further 

 attention. This is the great transverse commissure, or 

 Corpus Callosum, which, showing itself first in lower 

 Mammals, increases in size in higher members of the 

 series, till we find it attaining its maximum development 

 in the brain of Man. As stated in the last chapter, the 

 fibres of the Corpus Callosum pass across from Hemis- 

 phere to Hemisphere, so as to bring into relation corres- 

 ponding areas of convolutional Grey Matter. It does 

 not pass equally between all convolutions, but especially 

 between those which are also in relation with the great 

 basal ganglia (Broadbent). The Anterior Commissure, 

 though a morphologically distinct part, seems to have an 



