THE SPIRAL CORD. 



701 



gray matter and there break up into an arborization of nerve-fibrils which appears 

 to have some, though not direct, connection with a similar arborization of the 

 branched processes from the nerve-cells (see Fig. 411). 



The gray substance of the cord occupies its central part in the shape of two 

 crescentic horns, joined together by a commissure. Each of these crescents has 

 an anterior and posterior cornu. 



The posterior horn consists of two parts the caput cornu, or expanded 

 extremity of the horn (Fig. 409), round which is a lighter space or lamina of 



isr isar f i I 



Fissure. 



FK;. 409. Transverse section of the gray substance of the spinal cord through the middle of the lumbai 

 enlargement. On the left side of the figure" groups of large cells are seen ; on the right side, the course of the 

 fibres is shown without the cells. Magnified 13 diameters. 



gelatinous substance : and the cervix cornu, or narrower portion, which connects 

 it with the rest of the gray substance. 



The gelatinous substance is a peculiar accumulation of neuroglia (Klein), and 

 has been named by Rolando the substantia cinerea gelatinosa. 



The anterior horn of the gray substance in the cervical and lumbar swellings, 

 where it gives origin to the nerves of the extremities, is much larger than in any 

 other region, and contains several distinct groups of large and variously shaped 

 cells. 



In addition to this, in certain parts of the cord other horns or projections of 

 the gray matter may be seen on transverse section. One of these, the lateral 

 horn, is found projecting outward from the lateral region of the gray matter on a 

 level with the gray commissure in the cervical and upper part of the dorsal region 

 of the cord; and a second, Clarke's vesicular column, is found on the inner 

 side of the posterior horn near the gray commissure, in the upper cervical or 

 dorsal regions or at the point of exit of the lower lumbar nerves. 



The gray commissure is situated behind the white commissure, which sep- 

 arates it from the bottom of the anterior median fissure. 



The gray substance of the cord consists of (1) nerve-fibres of variable but 

 smaller average diameter than those of the columns ; (2) nerve-cells of various 

 shapes and sizes, with from two to eight processes ; (3) blood-vessels and 

 neuroglia. 



The nerve-fibres of the gray matter of the posterior horn are for the most part 



