SPINAL COED 227 



ture, and consists of two lateral masses and a connecting link, or 

 commissure. Near the central portion of the figure, a small cir- 

 cular opening occurs the transversely divided central canal. 



FIG. 147. HUMAN SPINAL CORD FROM THE DORSAL REGION, STAINED BY THE 

 WEIGERT-PAL METHOD. SLIGHTLY MAGNIFIED. PHOTOMICROGRAPH. 



is in communication, in the medulla, with the fourth ventri- 

 cle, and will serve as a starting point for our study. 



The gray matter completely surrounds the central canal, and 

 its outline resembles the capital H, or a pair of crescents with 

 their concavities looking outwards. The anterior (or ventral) 

 horns or cornua are blunt. The posterior (or dorsal) horns are 

 pointed. There are lateral projections from the anterior horns, 

 sometimes called lateral horns. They lie opposite the central 

 canal, and are most marked in the upper thoracic region. The 

 crescents are connected, a portion of the connecting substance 

 passing in front and a portion behind the central canal the 

 anterior and posterior gray commissural bands. The amount of 

 gray matter is greatest in the cervical and lumbar enlargements 

 of the cord (Fig. 148). 



The white substance is divided anteriorly by the anterior 

 median fissure, which cuts into the cord nearly to, but not quite 

 as far as the anterior gray commissure. A corresponding division 

 appears posteriorly (the posterior median fissure), which does not 

 divide the cord posteriorly, but the division is indicated by a band 

 of pia mater, which penetrates entirely to the posterior gray com- 

 missure. The two masses of white substance thus indicated are 

 roughly divided into anterior, lateral, and posterior columns by 



