THE NERVOUS SYSTEM 



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Gray Matter. — In the cross portion of the H is seen the central canal, 

 usually obliterated in the adult and represented only by a group of epithelial 

 cells. The central canal divides the gray matter connecting the two sides of the 

 cord into a ventral gray commissure and a dorsal gray commissure. Immediately 

 surrounding the epithelial cells is a light granular area composed mainly of 

 neuroglia and known as ihe central gelatinous substance. Toward the surface of the 



cord the posterior horn expands into a head or caput, external to which is an area 

 similar in general appearance to that surrounding the central canal, the gelatinous 

 substance of Rolando. The head is connected with the base of the dorsal horn 

 by a narrower neck or cervix. External to the gelatinous substance of Rolando 

 is a thin zone containing a plexus of fine medullated fibres (Weigert stain) known 

 as the marginal zone or zona spongiosa, and external to this, occupying the space 



