670 



THE CENTRAL AXIS OF THE NEltVOUS SYSTEM, 



the ependymis, connective tissue, nerve tubes, nerve cells, and vessels enter 

 into the structure of the medulla. 



The connective tissue of the spinal cord is very delicate, rich in nuclei, and 

 belongs to the variety that histologists have named " reticular " or" adenoid." 



It appears to arise from the pia mater, and forms lamellae that penetrate 

 the nerve-substance to meet and anastomose with each other, and finally 

 become confounded with the ependymis around the central canal. This 

 tissue, which is also named neuroglia, has been compared to a sponge, in 

 whose spaces are deposited the other elements of the cord. This neuroglia 

 exists in the white and grey substances, but is more abundant in the superior 

 than in the inferior grey cornua. It surrounds the upper extremity of the 

 former in becoming softer and more transparent, and is here designated the 

 gelatinous substance of Rolando (snbstantia gelatinosa\ It constitutes, in 

 great part, the grey commissure, and can be deeply stained by the corminate 

 of ammonia. 



TRANSVERSE SECTION OF SPINAL CORD OP MAN THROUGH THE MIDDLE OF THE 

 LUMBAR REGION, SHOWING ON THE RIGHT SIDE THE COURSE OF THE NERVE- 

 ROOTS, AND ON THE LEFT THE POSITION OF THE PRINCIPAL TRACTS OF VEHICULAR 

 MATTER. 



A, A, Anterior or inferior columns ; P, P, Posterior or superior columns ; L, L, Lateral 

 columns. a, Anterior or inferior median fissure ; jo, Posterior or superior median 

 fissure ; 6, 6, 6, 6, Anterior or inferior roots of spinal nerves ; c, c, Posterior or 

 superior roots ; <f, c?, 'Tracts of vesicular matter in anterior column; e, Tracts of 

 vesicular matter in posterior column ; /, Central canal ; g, Substantia gelatinosa. 



The tubes and cells form, with the neuroglia, the whole of the grey 

 substance. The cells have at least five prolongations, and the tubes are 

 reduced either to the axis-cylinder (axis-fibre), or to this and a very thin 

 layer of medullary substance. 



The cells are not uniformly distributed in the grey substance, but are 

 arranged in small masses that constitute three longitudinal columns : two 





