THE STRUCTURE OF THE SPINAL CORD. 



725 



of the ganglia further pluricordonal ganglia, whose neurites repeatedly send 

 divided fibers into the white columns of the same side (or after passing through 

 the commissure) of the opposite of the cord. 



The posterior horn contains in addition to the gelatinous substance of Rolando 

 (s.g.R.): (i) The exceedingly small, spindle-shaped ganglion-cells, whose neurites 

 pass into the posterior column, and whose intricately branched dendrites penetrate 

 the base of the posterior horn; (2) the rather superficial limiting cells situated 

 near the apex of the posterior horn, whose neurites pass through the gelatinous 

 substance into the lateral column; (3) star-shaped cells, whose dendrites in part 

 enter the column of Burdach, in part the gelatinous substance. 



The gray matter contains, in 

 addition to the ganglion-cells, an 

 exceedingly fine network of most 

 delicate nerve-fibers. This is formed 

 in part of intricately divided fine 

 fibers, the dendrites of the ganglion- 

 cells, but also of numerous fibrils 

 given off by the longitudinal axis- 

 cylinders present in all of the white 

 columns of the spinal cord. These 

 have been designated collaterals by 

 Santiago Ramon y Cajal. The ante- 

 rior columns send a rich network of 

 collaterals to the anterior horns; the 

 lateral columns to the region of the 

 columns of Clarke and the central 

 canal, and, in conjunction with the 

 collaterals from all three columns, 

 they form the posterior gray commis- 

 sure. The fibers of the posterior 

 columns send collaterals to the poste- 

 rior horn, the anterior horn, and the 

 columns of Clarke. 



The motor fibers passing through 

 the white columns of the spinal cord 

 give off numerous collaterals to the 

 gray matter throughout the entire 

 length from above downward to the 

 level at which the motor conduct- 

 ing tract reaches the motor cells of 

 the anterior horn by contact (Fig. 

 251, m.c). 



The neurites that form the ante- 

 rior roots give off collaterals to the 

 gray matter before they leave it. 



If a posterior root-fiber be 

 followed into the spinal cord, it 

 will be found to divide into an 

 ascending and a descending branch 

 in the posterior column. From both 

 of these branches, as well as from 

 the root-fiber itself, collaterals are 

 given off that enter the gray matter 



and terminate in arborescent rami- FIG. 251. 



fications (Fig. 251, s, c). The ex- 

 tremity of the descending branch forms a collateral in the gray matter of the 

 cord, that of the ascending branch a collateral in the medulla oblongata. 



The White Matter. All of the longitudinal nerve-fibers composing the white 

 matter of the columns of the spinal cord are arranged systematically, according 

 to their function, into separate bundles. 



Tiirck observed that after disease of certain portions of the brain the definite 

 tracts of fibers in the spinal cord were secondarily degenerated. P. Schieferdecker 

 confirmed this observation by animal experimentation. Finally, Flechsig dem- 

 onstrated that the fiber-systems in the spinal cord receive their myelin-sheaths 

 at different times in the process of development, and that those "fibers whose 



