1028 HUMAN ANATOMY. 



columns is, however, largely artificial, since neither superficially nor internally is there 

 a definite demarcation between these tracts. They may be, therefore, conveniently 

 regarded as forming a common antero-latcral column, that on each side embraces 

 something more than two-thirds of the semicircumference of the cord. In the lower 

 cervical and upper thoracic cord, each posterior column is subdivided by a shallow 

 furrow that lies from 1.5-^ mm. lateral to the posterior medium septum. This, the 

 paramedian sulcus i sulcus inter medius posterior;, corresponds in position with the 

 peripheral attachment of a radial septum of neuroglia that penetrates the white matter 

 for a variable distance, sometimes almost as far as the gray matter, and subdivides the 

 posterior column into two unequal tracts, of which the inner and smaller is the pos- 

 tero-median column ( fasciculus gracilis), or column of Goll, and the outer and 

 larger is the postero-lateral column ( fasciculus cuneatus), or column of Burdach. 

 The Gray Matter. Inspection of the transversely sectioned spinal cord, even 

 with the unaided eye, shows it to be composed of an irregular core of gray substance 

 enclosed by a mantle of white matter. Within each half of the cord the gray 



FIG. 885. 



-Posterior median septum 



asterior column 



./Posterior root-furrow 



Caput cornu - 



, 



iteral column 

 Cervix cornul 



.Posterior 

 root-fibres 



T_ EaSa Central canal 



Lateral cornu ~^B : 4 in gray 



commissure 



Basis cornu 



Caput comu 



Anterior median fissure Anterior column Anterior white commissure 



Transverse section of thoracic cord, showing disposition of gray and white matter and division of latter into 



:mti-ii.ii l.iti t.il and posterior columns. X 13. 



matter forms a comma-shaped area, the broader end of which lies in front and the 

 narrower behind, with the concavity directed laterally. The convex surfaces of the 

 tracts of the two sides, which look towards each other and the mid-line, are connected 

 by a transverse band of gray matter, the gray commissure ( commissura risea) that 

 extends across the mid-line, usually somewhat in advance of the middle of the sagittal 

 diameter, and encloses the minute central canal of the cord. By this canal the 

 connecting band, or central gray matter, is divided into a dorsal and a ventral part, 

 i\\t- posterior and the anterior ^ ray commissure, which lie behind and in front of the 



tube resprcti\ely. 



While the posterior median septum reaches the dorsal surface of the gray com- 

 missure, the ventral margin of the latter is separated from the anterior median fissure 

 by an intervening bridge of white matter, the anterior white commissure (com- 

 iiiisstira aiiu-iitu alba < which connects the anterior columns of the' cord and provides 

 an important pathway for fibres passing from one side to the other. A zone of mod- 

 ified neuroglia immediately surrounding the central canal is known as the Substantia 

 gelatinosa centralis < substantia 



