212 



THE NERVOUS SYSTEM. 



FIG. 82. 



layers (Fig. 82), which are not sharply marked off from one 

 another. Beneath the pia mater on the surface is a narrow molec- 

 ular zone, consisting of neuroglia, glia-cells, terminal branches 



of nerve- cell processes, and fine 

 medullated fibres running tan- 

 gentially or parallel to the surface. 

 Beneath this is a zone character- 

 ized by the presence of small 

 pyramidal nerve-cells. These are 

 long pyramidal cells, with their 

 apices directed toward the sur- 

 face. Each cell gives off an axis- 

 cylinder process from its base, 

 running (for the most part) into 

 the white matter beneath. From 

 the angles at the apex and base 

 of the cell are given off dend rites 

 which divide into branches in the 

 vicinity. This layer merges be- 

 low into a broad zone character- 

 ized by large pyramidal nerve- 

 cells, similar to those just de- 

 scribed, but of larger size. Be- 

 neath this zone is a layer contain- 

 ing polymorphous nerve-cells of 

 various shapes stellate, irregu- 

 lar, and fusiform. Neuroglia- 

 cells are scattered about among 

 the nerve-cells in the various 

 zones. 



The foregoing layers comprise 

 the cortical gray matter. Be- 

 neath them is the white matter of the interior, which at regu- 

 lar intervals sends slender, tapering bundles of medullated 

 fibres radiating into the lower layers of the gray matter. 



The ganglionic parts of the cerebrum, as the corpus striatum, 

 optic thalamus, corpora quadrigemina, olfactory bulb (or 

 nerve), consist of gray and white matter variously distributed, 

 with nerve-cells of various forms multipolar, stellate, fusi- 

 form, etc. 



Nerve-cells of cerebral cortex (Ca- 

 jal). 1, molecular zone ; 2, small 

 pyramidal nerve-cells ; 3, large 

 pyramidal cells ; 4, polymor- 

 phous cells ; 5, white matter. 



