THE CEREBRUM. 207 



5. The cuneus lies posteriorly to the quadrate lobule. It is a wedge- 

 shaped mass inclosed by the calcarine and parieto-occipital fissures. 



Structure. The gray matter of the cerebrum, about % of an 

 inch thick, is composed of five layers of nerve-cells : 



1. A superficial layer, containing a few small multipolar ganglion 

 cells. 



2. Small ganglion cells, pyramidal in shape. 



3. A layer of large pyramidal ganglion cells with processes running 

 off superiorly and laterally. 



4. The granular formation containing nerve-cells. 



5. Spindle-shaped and branching nerve-cells of a moderate size. 

 The white matter consists of three distinct sets of fibers. 



1. The diverging or peduncular fibers are mainly derived from the 

 columns of the cord and medulla oblongata ; passing upward 

 through the crura cerebri they receive accessory fibers from the 

 olivary fasciculus, corpora quadrigemina, and cerebellum. Some of 

 the fibers 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 fibers connect the two hemispheres, 

 through the corpus callosum and anterior and posterior com- 

 missures. 



3. The longitudinal commissural fibers connect different parts of the 

 same hemisphere. 



Functions. The cerebral hemispheres are the centers of the 

 nervous system through which are manifested all the phenomena of 

 the mind ; they are the centers in which impressions are registered 

 and reproduced subsequently as ideas ; they are the seat of intelli- 

 gence, reason, and will. 



However important a center the cerebrum may be for the exhibi- 

 tion of this highest form of nervous action, it is not directly essential 

 for the continuance of life, for it does not exert any control over 

 those automatic reflex acts, such as respiration, circulation, etc., 

 which regulate the functions 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, 

 i. Comparative anatomy shows that there is a general connection 



between the size of the brain, its texture, the depth and number 



