THE CENTRAL NERVOUS SYSTEM. 



255 



into two branches (Fig. 236, r). One of these ascends in the white 

 substance and the other descends. Both branches give off numer- 

 ous collaterals, which penetrate the gray matter, ending in teleneu- 

 rites associated with the teledendrites of the cells in both the ante- 

 rior and the posterior horns, and the column of Clarke. The main 

 branches of the sensory neurite also enter the gray matter, after 



Fig. 238. 



Fig. 239. 



Fig. 238— Diagram of the senso-rnotory reflex collaterals in the cord. (R. y Cajai.) a, gan- 

 glion-cell of the posterior nerve-root ; 6, division of its neurite into ascending and de- 

 scending branches ; c, collaterals to anterior horn ; d, terminal teleneurites in the pos- 

 terior horn ; e, motor cell of the anterior horn, with its processes. 



Fig. 239.— Longitudinal section of a part of the spinal cord, including a posterior nerve-root. 

 Semidiagrammatic. (R. y Cajal.) A, posterior nerve-root; S, white substance of the 

 cord ; 0, gray matter ; B, collateral teleneurites in the gray matter ; C, cell with a single 

 ascending neurite ; D, cell with bifurcating neurite, terminating at Fand /: E, cell with 

 a single descending neurite; F, G, terminal teleneurites ; a', collateral from a branch 

 of the posterior root-neurite ; b', collateral from the main neurite before its bifurcation. 



following the posterior column for a short distance, and end in tele- 

 neurites among the cells of the posterior horn and the substance of 

 Rolando. The collaterals which pass to the anterior horns (Fig. 

 237, H, and Fig. 238, c) have to do with the origin of reflex cen- 



