568 



NERVOUS SYSTEM 



J 



is quite distinctly divided into two layers, by a very delicate inter- 

 mediate layer of a whitish color. 



Histologists usually recognize four principal 

 layers in the cerebral cortex. An external (mo- 

 lecular) layer ; a layer of small pyramidal cells ; 

 a layer of large pyramidal cells ; a layer of 

 stellate cells. 



i. The molecular (superficial) layer presents 

 three kinds of cells lying beneath a layer of 

 neuroglia. The external cells of this layer are 

 small, and either bipolar or tripolar, the tripolar 

 cells resembling the cells 

 of the posterior layer of 

 gray matter of the spinal 

 cord. In the deepest por- 

 tion of this layer are large 

 polygonal cells. The neu- 

 rites of the cells of the 

 molecular layer have rela- 

 tions with the teloden- 

 drites of the deeper layers 

 and with their own teloden- 

 drites, but these neurites 

 (R. y Cajai). do not extend to the white 



I, molecular layer; 2, the matter, 

 layer of small pyramidal cells; . 



3, layer of large pyramidal 2 - J- n ^ layer OI Small 



cells; 4, layer of large stellate pyramidal Cells IS the 

 cells; 5, white substance. 



most important and the 



thickest of the three. These cells present one 

 bifurcating neurite and many dendrites and col- 

 laterals. This layer also contains a few large 

 pyramidal cells, with neurites, dendrites, teloneu- 

 rites and telodendrites. 



3. The layer of large pyramidal cells has 

 the same arrangement as that of the cells of the 



Fig. 136. Cells of the 

 molecular layer of the cerebral 

 cortex (R. y Cajal). 



A, C, small spindle-shaped 



second layer. This layer also contains a few small ceils; B, small stellate ceil; 

 pyramidal cells. The second and third layers are ^'J^f Ste " ate ^ * * 

 not very easily separable from each other. 



4. This layer presents" rather large stellate cells, with neurites, den- 

 drites and collaterals. 1 



1 Some histologists describe five layers in the cerebral cortex, adding to the four layers 

 described above, a layer external to the molecular layer; but this layer is composed largely of 

 neuroglia and does not contain nerve-cells. 



