252 



NORMAL HISTOLOGY. 



column of the white matter, between the posterior cornua and the 

 posterior median fissure, conduct, for the most part, centripetal 

 impulses. Impulses having the same upward direction are also 

 conveyed by the direct cerebellar tract and the tract of (lowers in 

 the lateral column of the white matter. Centrifugal impulses, 

 motor stimuli, are conveyed by the fibres in the direct pyramidal 

 tract of the anterior column and by those of the crossed pyramidal 



Diagram of spinal cord, illustrating the associations of its various nervous elements. (R. y 

 Cajal.) a, collateral from Goll's tract, entering into the formation of the posterior com- 

 missure ; b, collateral to the posterior horn ; c, collateral to the formatio reticularis and 

 the anterior horn ; d, posterior nerve neurite, with its collaterals ; e, collaterals from the 

 lateral column ; /, collaterals to the anterior commissure ; g, central canal ; h, neurite in 

 the crossed pyramidal tract from the commissure-cell of the opposite side ; ?', its course 

 in the commissure ; j, neurite from a large motor cell in the anterior horn k ; I, cell of 

 the anterior horn, giving off a neurite dividing into an ascending and a descending 

 branch (compare Fig. 239, D) ; m, commissure-cell ; n, cell giving off a collateral within 

 the gray matter ; o, neurite of the cell u, in Clarke's column ; p, neurite from the mar- 

 ginal cell 8, of the substance of Rolando ; q, cross-section of an axis-cylinder (neurite) 

 in the white substance of the cord ; r, division of a posterior nerve-fibre (neurite) into 

 ascending and descending branches; t, small cell in the substance of Rolando. Aside 

 from the cells indicated in the figure, the gray matter contains some that give off neurites 

 which divide into two or three branches while in the gray matter, the branches going 

 to different columns of white matter. There are also cells with very short neurites, 

 which terminate in teleneurites within the gray matter, and probably distribute nervous 

 impulses for short longitudinal distances. 



tract in the lateral column. The tracts hitherto considered contain 

 fibres that are continued into the higher nerve-centres of the brain 

 and cerebellum, to or from which they convey nervous impulses. 

 But the spinal cord is not merely a collection of such transmitting 



