SPINAL CORD. 471 



Fissures (Fig. 270). On the anterior surface of the spinal 

 cord is a groove, the anterior median fissure, which extends to the 

 anterior white commissure. On the posterior surface is also a so- 

 called fissure, the posterior median fissure, which is filled with 

 connective tissue and blood-vessels, and extends to the posterior 

 gray commissure. It will thus be seen that the anterior and 

 posterior fissures nearly divide the cord into two symmetrical 

 halves, which are connected by the commissures.. 



At a little distance from the anterior median fissure on each 

 side is the anterolaterai fissure. Strictly speaking, this is not a 

 fissure, being rather a line of small openings at which emerge the 

 anterior roots of the spinal nerves. In front of the posterior 

 median fissure and on either side is the poster -olateral fissure. Here 

 emerge the posterior roots of the nerves. The posterior intermedi- 

 ate furrow is between the posterior median and posterolateral 

 fissures. 



Columns. The anterior and posterior median fissures divide 

 the cord into two symmetrical halves, and the anterolaterai and 

 posterolateral fissures subdivide each half into three columns 

 called main columns: anterolaterai, posterolateral, and posterior 

 median. 



Anterolaterai Column. This includes that portion of the cord 

 between the anterior median and the posterolateral fissure. It is 

 divided by some anatomists into an anterior, situated between the 

 anterior median fissure and the anterior nerve-roots, and a lateral, 

 the portion between these roots and the posterolateral fissure 

 (Fig. 271). 



Posterolateral Column. This is the portion between the postero- 

 lateral fissure and the posterior intermediate furrow. 



Posterior Median Column. This is also called posteromedial 

 column. It is situated between the intermediate furrow and the 

 posterior median fissure. The posterolateral and posterior median 

 are sometimes described together as the posterior column. 



Section of the Spinal Cord (Fig. 273). A cross-section of 

 the spinal cord shows a central gray substance and an external 

 white substance. The gray matter presents the appearance of two 

 crescents, with the concavities outward, joined together by a band 

 of gray matter, the gray commissure. The points of the crescents 

 are the horns or cornua, two anterior and two posterior. The 

 posterior cornua come nearly to the surface of the cord at the 

 posterolateral fissure, while between the surface and the extremi- 

 ties of the anterior cornua there is considerable white matter. 

 The arrangement of the white matter into columns is readily 

 discerned in this section. In the gray commissure is a small 

 canal the central canal which communicates with the fourth 

 ventricle of the brain, and contains cerebrospinal fluid. This 

 is a colorless alkaline fluid containing sodium chlorid and other 



