THE CENTRAL NERVOUS SYSTEM. 



251 



Fig. 2:15. 



POSTERIOR 

 ROOT 



Transverse section of human spinal cord, from the middle lumbar region. (Schafer.) a b, c, 

 groups of ganglion-cells in the anterior horn ; d, cells of the lateral horn ; e, middle 

 group of cells ; /, cells of Clarke's column ; g, cells of posterior horn ; c. c, central canal ; 

 a, c, anterior commissure of white matter. 



In cross-section this column of gray matter presents a transverse 

 central portion, the gray commissure, near the middle of which is 

 the central canal. At each side this gray commissure blends with 

 masses of gray matter, occupying nearly the centre of each lateral 

 half of the cord and having a general crescentic form. The ends 

 of these crescentic masses form the anterior and posterior cornua 

 of the gray matter, from which the anterior and posterior roots of 

 the spinal nerves proceed. The anterior cornua are larger than the 

 posterior and contain larger ganglion-cells. 



Surrounding the column of gray matter everywhere, except at 

 the bottom of the posterior median fissure of the cord, and the 

 interruptions formed by the nerve-roots in their exit from the gray 

 matter, is a laver of white matter, formed of medullated nerve- 

 fibres running parallel with the axis of the cord and held together 

 by neuroglia and delicate vascularized fibrous bands proceeding 

 from the deep surface of the pia mater. 



The white matter of the cord has been divided into a number of 

 •columns, for the most part indistinguishable through structural dif- 

 ferences, but each containing fibres that play similar functional roles. 

 These columns, with their names, are indicated in Figs. 233, 234, 

 and 235. The columns of Goll and Burdach, forming the posterior 



