478 



THE BRAIN. 



VERTICAL SECTION OF ONE OP THE CE- 

 REBRAL CONVOLUTIONS ; showing pyramidal 

 cells, and bundles of fibres passing outward from 

 the white substance. Magnified 300 diameters. 

 (Henle.) 



portion of the layer of gray 

 substance, the cells are distin- 

 guished by their pyramidal 

 form ; the pointed extremity of 

 the cell being, with few excep- 

 tions, directed toward the surface 

 of the brain, and the base toward 

 the white substance of the inte- 

 rior. According to Henle, they 

 have an average diameter of 15 

 mmm. Two, three, or sometimes 

 even four prolongations extend 

 from the angles at the base of 

 the cell, running inward toward 

 the white substance, and be- 

 coming more or less divided and 

 ramified ; while the pointed ex- 

 tremity, on the other hand, ex- 

 tends outward in a single pro- 

 longation toward the cerebral 

 surface. 



The fibres, as they penetrate 

 from the white into the gray 

 substance, are arranged in bun- 

 dles, where they at first run in 

 a general direction parallel with 

 each other. But these bundles 

 rapidly diminish in size, as the 

 fibres diverge laterally to pursue 

 a more or less horizontal course ; 

 and in the external portions of 

 the gray substance there are 

 only isolated fibres running in 

 various directions. In the gray 

 substance, the nerve fibres be- 

 come reduced to their smallest 

 dimensions, measuring, accord- 

 ing to Kolliker, from about 1 to 

 2 mmm. in diameter. Some of 

 them spread out at various levels 

 in the cortical layer, while others 

 continue a vertical or oblique 

 course quite to the superficial 

 portions of the gray substance. 



The immediate relation be- 

 tween the fibres and cells of the 

 gray substance of the hemi- 

 spheres has not been determined 





