560 



THE SENSORIAL FUNCTIONS. 



reception and defence of this most important 

 organ. It is chiefly from the expansion of the 

 hemispheres, and the developement of its convo- 

 lutions, that the human brain derives this great 

 augmentation of size.* 



* This will be apparent from the vertical section of the human 

 brain, Fig. 461 ; where, as before, s is the spinal marrow; m, 

 the medulla oblongata; c, the cerebellum, with the arbor vitce ; 

 T, the optic tubercles, or corpora quadrigemina, dwindled to a 

 very small size, compared with their bulk in fishes ; p, the 

 pineal gland, supposed by Des Cartes to be the seat of the 

 soul; V, one of the lateral ventricles; q, the corpus callosum; 

 and H, H, H, the hemispheres. 



Several expedients have been proposed for estimating the 

 relative size of the brain in different tribes of animals, with a 

 view of deducing conclusions as to the constancy of the relation 

 which is presumed to exist between its greater magnitude and 

 the possession of higher intellectual faculties. The most cele- 

 brated is that devised by Camper, and which he termed the 

 facial angle, composed of two lines, one drawn in the direction 



