590 



NERVOUS SYSTEM. 



The cord is marked by an anterior and a posterior median fissure, and 

 by imperfect and somewhat indistinct anterior and posterior lateral grooves, 



FIG. 216. Transverse section of the spinal cord of a child six months old, at the middle of the lumbar 

 enlargement, treated with potassium-auric chloride and uranium nitrate ; magnified 20 diame- 

 ters. By means of these reagents, the direction of the fibres in the gray substance is rendered un- 

 usually distinct (Gerlach). 



a, anterior columns ; 6, posterior columns ; c, lateral columns : d, anterior roots ; e, posterior roots ; /, 

 anterior white commissure, in communication with the fasciculi of the anterior cornua and the an- 

 terior columns ; g, central canal with its epithelium ; /i, surrounding connective substance of the 

 central canal ; i, transverse fasciculi of the gray commissure in front of the central canal ; k, trans- 

 verse fasciculi of the gray commissure behind the central canal ; I, transverse section of the two 

 central veins ; m, anterior cornua ; n, great, lateral cellular layer of tl anterior cornua ; o, lesser, 

 anterior cellular layer ; p, smallest, median cellular layer ; g, posterior cornua ; r, ascending fas- 

 ciculi in the posterior cornua ; s, substantia gelatinosa. 



from which latter arise the anterior and the posterior roots of the spinal 

 nerves. The posterior lateral groove is tolerably well marked, but there is 

 no distinct line at the origin of the anterior roots. The anterior median fis- 

 sure is perfectly distinct. It penetrates the anterior portion of the cord, in 

 the median line, for about one-third of its thickness and receives a highly vas- 

 cular fold of the pia mater. It extends to the anterior white commissure. 

 The posterior fissure is not so distinct as the anterior, and it is not lined 

 throughout by a fold of the pia mater, but is filled with connective tissue 

 and blood-vessels, which form a septum posteriorly, between the lateral 

 halves of the cord. The posterior median fissure extends nearly to the cen- 

 tre of the cord, as far as the posterior gray commissure. 



The arrangement of the white and the gray matter in the cord is seen in a 

 transverse section. The gray substance is in the form of a letter H, present- 

 ing two anterior and two posterior cornua connected by what is called the 

 gray commissure. The anterior cornua are short and broad, and they do not 



