124 



NERVOUS SYSTEM. 



FIG. 35. 



face which is within the longitu- 

 dinal fissure is 'marked by sulci 

 and convolutions. The convolu- 

 tions of the frontal, parietal, and 

 occipital lobes are found here, 

 and the margined (or calloso- 

 marginal) convolution, lying 

 above the corpus callosum, is 

 the principal landmark. 



How is the gray matter of the 



cerebrum arranged? 

 The increase in the area of 

 the surface of the hemispheres 

 by the infolding of the sulci 

 adds very greatly to the amount 

 of gray substance in the brain ; 

 for the entire surface is com- 

 posed of gray substance, and this 

 follows the sulci and fissures 

 (Fig. 34) in all their folds, and 

 is not cut into by them. Be- 

 sides the gray matter in the con- 

 volutions there are certain other 

 gray masses in the substance of 

 the white matter : the optic 

 thalami, the corpora striata, and 

 the claustrum (Fig. 34) are the 

 chief of these gray masses. 



What is the minute structure 

 of the gray matter of the 

 cortex ? 



The gray matter of the cortex 

 is made up of ganglion-cells of 

 various shapes and sizes lying in 

 a loose connective-tissue stroma. 

 The connective tissue is more 

 abundant at the surface. The 

 cells are the source of numerous 

 nerve-fibres which pass out into 

 the white matter (Fig. 35). There 

 are counted five layers of these 



Gray Matter of the Cerebral Cortex (-Meynert).ganglionic tissues, and, while 



