STRUCTURE OF THE SPINAL CORD 



189 



nerve-cells at the base of the posterior cornu (Clarke's column]. 

 Another group is seen on the outer side of the grey matter lying in a 

 projection which is sometimes known as the lateral cornu (inter medio- 

 iateral tract). This also is only distinct in the dorsal region. The 

 cells of the posterior cornu are not collected into a, special group. 



Course of the nerve-roots in the spinal cord. The anterior roots 

 enter the anterior cornu in a number of bundles (fig. 224, a, a}. Some 

 of their fibres (i, i) are directly connected with the nerve-cells there, 

 others pass through the grey matter into the posterior cornu, others into 



FIG. 224. DIAGRAM TO IL- 

 LUSTRATE THE PROBABLE 

 COURSE TAKEN BY THE FI- 

 BRES OF THE NERVE-ROOTS 

 ON ENTERING THE SPINAL 

 CORD. 



, , two bundles of the anterior 

 root of a nerve ; 1, 1, some of 

 tbeir fibres passing into the 

 lateral cells of the anterior 

 cornu; 1', 1', others passing 

 into the mesial cells of the 

 same cornu ; 2, 2, fibres passing 

 to the lateral column of the 

 same side without joining 

 nerve-cells; 3, 3, fibres passing 

 towards the posterior cornu ; 

 4, 4, fibres passing across the 

 anterior commissure, to enter 

 nerve-cells in the anterior conm 

 of the other side ; p, bundle 

 of the posterior root ; />, I, fibres 

 of its lateral or external division 

 coming through and around 

 the gelatinous substance of 

 Rolando ; some of these, 5, are 

 represented as becoming longi- 

 tudinal in the latter; others, 

 6, 6, as passing towards the 

 anterior cornu, either directly 

 or after joining cells in the posterior cornu, and others, 7, as curving inwards towards the grey 

 commissure ; />, m. fibres of the mesial or inner division, entering the posterior column and then 

 becoming longitudinal ; ;/, m 1 , fibres from a posterior root which had joined the cord lower down 

 and entered the posterior column, now passing into the grey matter at the root of the posterior 

 cornu. Of these, 8 is represented as entering Clarke's column, 9, as curving around this and cours- 

 ing to the anterior commissure, and 10 as passing towards the anterior cornu. The axis-cylinder 

 processes of the cells of Clarke's column are shown arching round, and taking the direction of the 

 lateral column. .m/., anterior median fissure ;p.mj., posterior median fissure ; c.c., central canal; 

 S.R: substantia gelatinosa of Rolando. 



the lateral white column of the same side of the cord (2, 3), and others 

 again pass across in the isthmus to the anterior cornu of the opposite 

 side (4). 



The fibres of the posterior roots (fig. 224, p] chiefly pass into the 

 posterior white columns, from which after a short course they enter 

 the grey matter and are partly connected with its cells, and partly pass 

 to the other side of the cord. Some of the fibres of the posterior 

 roots enter the posterior cornu directly, and are believed to be con- 

 nected with the scattered cells of that cornu. 



The central canal of the spinal cord is lined by columnar ciliated 

 epithelium-cells, which are surrounded by a quantity of neuroglia. 



