472 



THE NERVOUS SYSTEM. 



inorganic salts, and about 0.1 per cent, of proteids, principally 

 proto-albumose, with some serum-globulin, and rarely peptone. 

 Serum-albumin, fibrinogen, and nucleoproteid are absent. It also 

 contains a non-nitrogenous reducing substance considered by 

 Claude Bernard to be sugar, but by Halliburton to be pyrocatechin 

 derived from the proteids. 



The central canal is lined with columnar epithelium, which in 

 fetal life is ciliated, but the cilia are often absent in the adult. 

 The canal is of special interest in connection with the develop- 

 ment of the cord. Sections of the cord at different levels show 

 that the white substance is most abundant in the upper part, and 



FIG. 273. Transverse section of half the spinal cord, in the lumbar enlargement 

 (semi-diagrammatic) : 1, anterior median fissure ; 2, posterior median fissure; 3, cen- 

 tral canal lined with epithelium ; 4, posterior commissure ; 5, anterior commissure ; 

 6, posterior column ; 7, lateral column ; 8, anterior column (the white substance is 

 traversed by radiating trabeculse of pia mater) ; 9, fasciculus of posterior nerve-root, 

 entering in one bundle ; 10, fasciculi of anterior roots, entering in four spreading 

 bundles of fibers ; b, in the cervix cornu, decussating fibers from the nerve-roots 

 and posterior commissure; c, posterior vesicular columns. About half-way between 

 the central canal and 7 is seen the group of nerve-cells forming the tractus inter- 

 mediolateralis ; e, e, fibers of anterior roots; e', fibers of anterior roots which 

 decussate in anterior commissure (Allen Thomson). 



gradually becomes less abundant as the examination is made down 

 the cord. The cervical and lumbar enlargements are due to the 

 increased amount of gray matter at these points. 



Minute Structure of the Cord. Neuroglia supports both 

 the white and the gray matter of the spinal cord, and occurs also 

 under the pia mater, around the central canal, forming the sub- 

 stantia gelatinosa centralis, and at the apex of the posterior horn, 

 forming the substantia cinerea gelatinosa of Rolando or substantia 

 gelatinosa lateralis. 



The white substance is made up of medullated nerve-fibers and 

 blood-vessels, in addition to neuroglia. The medullated nerve- 



