1 86 HUMAN PHYSIOLOGY. 



1. The paracentral convolution, lying in the region of the upper extremity 

 of the fissure of Rolando; it contains the large giant cells of Betz. Injury 

 to this convolution is followed by degeneration of the motor tract. 



2. The callosal convolution, lying below the supercallosal fissure. Running 

 parallel with the corpus callosum, it terminates at its posterior border in the 

 hippocampal gyrus. 



3. The gyrus hippocampus is formed by the union of the preceding con- 

 volution with the occipitotemporal. It runs forward and terminates in a 

 hooked extremity uncus. 



4. The quadrate lobule, or proecuneus, lies between the upper extremity of the 

 callosomarginal fissure and the parieto-occipital. 



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

 mass inclosed by the calcarine and occipital fissures. 



Structure. The gray matter of the cerebrum, about J 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 super- 

 iorly 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 quadri- 

 gemina, 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 trasverse commissural fibers connect the two hemispheres, through the 

 corpus callosum and anterior and posterior commissures. 



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 subse- 

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



However important a center the cerebrum may be for the exhibition 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 respiraton, circulation, etc., which regulate the functions of organic life. 



