THE CEREBRAL CORTEX 



569 



It may be said in general terms that the more superficial cells of the 

 cerebral cortex are small and the deeper cells are larger. The neurites 

 of the molecular layer do not pass to the white matter. The neurites of 

 the three deeper layers extend downward into the white matter. The 

 dendrites and telodendrites pass, some upward to the molecular layer, 

 and some to interlace with each other. 



Fig. 137. Diagrammatic section through the 

 cerebral cortex (R. y Cajal). 



A, small pyramidal cell of the second layer ; 



B, two large pyramidal cells of the third layer; 



C, D, stellate cells of the fourth layer; E, centrip- 

 etal neurite from distant centres ; F, collaterals 

 from the white substance ; G, bifurcated neurite 

 from the white substance. 



Fig. 138. Cells with short neurites in the cerebral 

 cortex (R. y Cajal). 



A, molecular layer; B, white substance; a, 

 cells with neurites and teloneurites ; b, cell with 

 a neurite extending downward ; c, c, cells with 

 neurites extending upward; d, small pyramidal 

 cell. 



The cerebral cortex receives centripetal fibres from the white matter, 

 which give off abundant collaterals and terminate in the molecular 

 layer by arborizing filaments (synapses) surrounding the nerve-cells. 



The white matter of the cerebrum presents four groups of fibres : 



1. Centrifugal, or " projection " fibres pass downward from the 

 three deeper layers of the cortex and finally, with their collaterals, 

 extend into the pyramidal tracts of the cord. 



2. Commissural fibres from the smaller pyramidal cells of the cortex 

 connect the two sides of the cerebrum. 



