724 



THE STRUCTURE OF THE SPINAL CORD. 



as the longitudinal fibers entering the columns from the gray matter, have in part 

 a transverse and in part an oblique course. In the anterior white commissure, 

 fibers passing in a transverse direction decussate. 



The gray matter exhibits in cross-section the anterior horns (co.a), from 

 which, on each side, the anterior roots of the spinal nerves arise; also the pos- 

 terior horns (co.p), with the incoming posterior roots (r.p); and in addition the 

 smaller lateral horns (co.l). In the anterior horn the following groups of 

 cells can be distinguished: (i) The large root-cells (a) situated anteriorly and 

 laterally, from whose neurites the anterior roots arise directly. The dendrites 

 of these cells pass into the anterior and lateral columns, and in part also into 

 the anterior white commissure. (2) The commissural cells (6), principally ante- 

 rior and median in situation, but in part also in the gray matter, which send 

 their neurites through the anterior white commissure to the opposite side, where 

 they divide into an ascending and a descending branch. 



-fa. 



co.a. 



FIG. 250. Transverse Section of the Spinal Cord at the Level of the Eighth Dorsal Nerve, X 10 (after Schwalbe). 

 s.a, Anterior longitudinal fissure; s.p, posterior septum, occupying the posterior longitudinal fissure; c.a, 

 anterior commissure; s.g.c. central gelatinous substance; c.c, central canal; c.p, posterior commissure; v, 

 vein; co .a, anterior horn; co.l, lateral horn, and behind it the reticular process; co.p, posterior horn; a, antero- 

 f c nr anterior median group of ganglion-cells; c, cells of the lateral horn; d, cells of the columns 



oi bulling and Clarke; e, solitary cells of the posterior horn; r.a, anterior root; r.p, posterior root; /, its 

 posterior-horn bundle; /', posterior-column bundle; /", longitudinal fibers of the posterior horn; s.g.R, gelat- 

 inous substance of Rolando; /.a, anterior column; /./, lateral column; f.p, posterior column. 



The lateral horns contain the so-called column-cells (co.l), that is small ganglia 



whose neurites form short connecting tracts between groups of cells at different 



levels of the cord. These connecting tracts are situated in the anterior, posterior 



and lateral white columns (Fig. 252, b, f, d), and they serve for the conduction of 



extensive coordinated reflexes. Internal to the origin of the posterior horns, 



adjacent to the posterior commissure, is situated a group of cells forming the column 



: btillmg and Clarke (d) . This group of cells is plainly visible from the lower 



extremity of the cervical to the beginning of the lumbar enlargement, and its 



leuntes pass partly in the direct cerebellar tract, and partly to the anterior 



white commissure. 



In addition there are in the anterior portion of the gray matter ganglia with 

 Hart neurites whose complex ramifications terminate in the immediate vicinity 



