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ANATOMY AND PHYSIOLOGY 



The white portion is composed of white fibers. They run in 

 many directions. Some connect the different main divisions of 

 the brain; others run from one part of the cortex to another; 

 others still, in great number, connect the brain and spinal cord 

 (Fig. 192). Taken together, they make up the mass of the brain 

 itself. 



The brain has four principal parts, the cerebrum, cerebellum, 

 medulla oblongata, and pons Varolii. 



FIG. 192. 



The letters mark white fibers. They connect the cortex with other parts, also 

 different parts of cortex together. Many fibers are seen to pass through the basal 

 ganglia. The Roman numerals indicate nerves. (Brubaker, after Starr.) 



The cerebrum is the largest division and occupies nearly the 

 whole cranial vault. It is divided into two hemispheres, right and 

 left, by a longitudinal fissure. At the bottom of this fissure white 

 fibers are seen to pass from one side to the other, thus forming a 

 transverse commissure, connecting the hemispheres, and called the 

 corpus callosum (Fig. 193). Each hemisphere is marked off by 

 specially deep fissures, into lobes, the principal ones being the 

 frontal, parietal, occipital, and temporal. The principal fissures 

 between the lobes are: the fissure of Rolando between the frontal 

 and parietal; the parieto-occipital, between the parietal and occi- 



