CENTRAL ORGANS OF NERVOUS SYSTEM. 



219 



front of this exists a crossing of nervous fibres, the commis- 

 sura anterior (f) ; behind the axis canal we meet with a pre- 

 dominantly connective-tissue mass, the so-called commissura 

 posterior (h). The white investing substance presents the 



Fig. 187. — Transverse section through the lower half of the human spinal cord : a, central 

 canal ; 6, fissura anterior : c, fissura posterior ; d, anterior horn, with the considerable ganglion 

 cells ; e, posterior horn, with the smaller ones ; f, anterior white commissure ; g, frame-work sub- 

 stance around the central canal; k, posterior gray commissure; i, bundles of the anterior, and k, 

 posterior spinal roots ; /, anterior, vi, lateral, and «, posterior column. 



anterior column (/), the lateral (in), and the posterior (n), 

 consisting essentially of longitudinally arranged medullated 

 nerve fibres. At the margin of the anterior and lateral col- 

 umns, the motory roots of the spinal nerves pass through to 

 the gray substance (i) ; between the middle and posterior 

 systems of columns we perceive, shining through, the poste- 

 rior sensory roots of these nerves (k). 



A delicate connective tissue permeates the whole organ as 

 a supporting and frame-work substance. It is the bearer of 

 the nutritive system of blood-vessels. 



Let us first discuss this connective-tissue substratum. 



