126 HUMAN PHYSIOLOGY. 



columns of the cord and medulla oblongata ; passing upward through the 

 crura cerebri, they receive accessory fibres from the olivary fasciculus, cor- 

 pora quadrigemina and cerebellum. Some of the fibres terminate in the 

 optic thalami and corpora striata, while others radiate into the anterior 

 middle and posterior lobes of the cerebrum. 



2. The transverse commissural fibres connect together the two hemi- 

 spheres, through the corpus callosum and anterior and posterior commis- 

 sures. 



3. The longitudinal commissural fibres connect together different parts 

 of the same hemisphere. 



Functions. The cerebral hemispheres are the centres of the nervous 

 system through which are manifested all the phenomena of the mind ; 

 they are the centres in which impressions are registered, and reproduced 

 subsequently as ideas; they are the seat of intelligence, reason and will. 



However important a centre the cerebrum may be, for the exhibition of 

 this highest form of nervous action, it is not directly essential for the con- 

 tinuance of life ; for it does not exert any control over those automatic 

 reflex acts, such as respiration, circulation, etc., which regulate the func- 

 tions of organic life. 



From the study of comparative anatomy, pathology, vivisection, etc., 

 evidence has been obtained which throws some light upon the physiology 

 of the cerebral hemispheres. 



1. Comparative Anatomy shows that there is a general connection be- 

 tween the size of the brain, its texture, the depth and number of convolu- 

 tions, and the exhibition of mental power. Throughout the entire animal 

 series, the increase in intelligence goes hand in hand with an increase in 

 the development of the brain. In man there is an enormous increase in 

 size over that of the highest animals, the anthropoids. The most cultivated 

 races of men have the greatest cranial capacity; that of the educated 

 European being about 116 cubic inches, that of the Australian being about 

 60 cubic inches, a difference of 56 cubic inches. Men distinguished for 

 great mental power usually have large and well-developed brains; that of 

 Cuvier weighed 64 ozs.; that of Abercrombie 63 ozs.; the average being 

 about 48 to 50 ozs.; not only the size, but above all, the texture of the 

 brain, must be taken into consideration. 



2. Pathology. Any severe injury or disease disorganizing the hemi- 

 spheres is at once attended by a disturbance, or entire suspension of mental 

 activity. A blow on the head producing concussion, or undue pressure 

 from cerebral hemorrhage destroys consciousness; physical and chemical 

 alterations in the gray matter have been shown to coexist with insanity, 



