THE STRUCTURE OF THE SPINAL CORD. 



539 



480. The tracts of white matter. At first sight the white matter of the 

 cord appears to be of uniform nature. We can use the nerve-roots to 

 delimitate the anterior, posterior, and lateral columns, but \ve appear to 



FIG. 122. 



Transverse Dorso-ventral Section of the Spinal Cord (Human) at the Level of the Third Lum- 

 bar Nerve. (Sherrington.) This is drawn to the same scale as Figs. 119, 120, and in the same 

 way, except that the outline of the gray matter is not exaggerated, Pr'. median; Pr. interme- 

 diate ; Pr". lateral bundles of posterior roots. The region comprised under m.t. is the marginal 

 zone of Lissauer's zone. The other letters of reference are the same as in Figs. 119, 121. The 

 three figures, 119, 121, 122, are intended to illustrate the main differential features of the cervical, 

 thoracic, and lumbar cord. 



have no criteria to distinguish parts in each column. In the cervical and 

 upper thoracic regions of the cord, a septum (Fig. 119, .) in the posterior 

 column, somewhat more conspicuous than the other septa, has enabled 

 anatomists to distinguish an inner median portion, the median posterior 



