THE CENTRAL NERVOUS SYSTEM. 



261 



Fig. 243. 



lying layers, which form arborescent expansions in the molecular 

 layer, similar to those of the cells of Purkinje in the cerebellum, 

 extending to the surface of the gray matter. 



The large stellate cells of the molecular layer (Fig. 244, D) send 

 their dendrites in various directions into 

 the molecular layer and the layer of 

 small pyramidal cells lying beneath it. 

 The neurite is distributed in the molec- 

 ular and upper portions of the under- 

 lying layers, but is never extended into 

 the white matter. The dendrites of these 

 cells come into relations with the neurites 

 of the other cells of this layer and with 

 those that proceed upward from some of 

 the cells in the deeper layers. 



The small spindle- and stellate cells 

 (A, B, C, Fig. 244) are considered to be 

 the autochthonous cells of the cerebral 

 cortex — i. e., the cells of the brain in 

 which the highest order of nervous im- 

 pulses find their origin. The small 

 spindle-shaped cells, with their peculiar 

 neurites, are extremely abundant and 

 fill the molecular layer with a mass 

 of interwoven filaments. 



The second and third layers of the 

 cerebral gray matter are characterized 

 by the presence of pyramidal nerve- 

 cells of various sizes, the smaller being 

 relatively more abundant in the second 

 layer and the larger in the third layer. From the apex of the pyram- 

 idal cell a stout, " primordial " dendrite passes vertically into the 

 molecular layer, where, as well as during its course to the molecular 

 layer, it gives off numerous branches, and finally ends in a brush of 

 teledendrites extending to the surface of the gray matter (Fig. 245, 

 A, B). Other and shorter dendrites are given off from the body of the 

 cell, which ramify and end in the second, third, or fourth layer of the 

 gray matter. The neurites from the bases of the pyramidal cells pass 

 vertically downward into the white substance, where they may 

 bifurcate, giving axis-cylinders to two nerve-fibres. While within 



j s 



Vertical section of the cerebral cor- 

 tex, showing its layers. (R. y 

 Cajal.) 1, molecular layer; t, 

 layer of the small pyramidal 

 cells ; 3, layer of the large pyram- 

 idal cells ; 4, layer of polymor- 

 phic cells ; 5, white matter. 



