418 



THE NERVOUS SYSTEM. 





(5). At this situation, accord- 

 ingly, the gray substance of the 

 cortex is in close proximity to 

 that of the cerebral ganglia, while 

 elsewhere it is separated from 

 them by a considerable thickness 

 of white substance. 



Gray Substance of the Convo- 

 lutions. The gray substance on 

 the surface of the hemispheres 

 forms a convoluted layer, into 

 which the nerve fibres penetrate 

 from the central mass of white 

 substance. It consists of a uni- 

 formly granular matrix, in which 

 are imbedded nerve cells and their 

 prolongations, together with the 

 nerve fibres dispersed among 

 them. It is divided into several 

 superimposed layers, distinguish- 

 ed by the form, size, and numbers 

 of the nerve cells which they 

 contain. The most characteristic 

 of these elements are the so- 

 called "pyramidal cells," occupy- 

 ing the middle portion of the gray 

 substance. They have a pointed 

 extremity, directed outward, 

 while the base looks toward the 

 white substance of the interior. 

 The most superficial of these cells 

 are the smallest and most numer- 

 ous, averaging about 10 mmm. in 

 diameter. Those which are more 

 deeply seated are less abundant, 

 but of larger size, from 25 to 

 40 mmm. in diameter. Some of 

 the prolongations from the base 

 of the cells lose themselves 

 in the bundles of nerve fibres 

 entering from the white sub- 

 stance. 



Beneath the pyramidal cells is 

 a laver containing much smaller 



VERTICAL SECTION OF ONE OF THE CEREBRAL CON- Cellular elements, from 8 to 10 



VOLUTIONS; showing pyramidal ceils, and bun- mmm . in diameter, known as the 



dies of fibres passing outward from the white 



substance. Magnified 300 diameters. (Henle.) nuclear layer." Its Cells have 



