SPINAL CORD. 



505 



a variable length become superficial. The longitudinal fibres are more superficial, run nearly 

 parallel with each other, and form the greater portion of the white columns. 



The gray substance of the cord con- 

 sists of, 1. Nerve fibres of variable, but 



smaller, average diameter than those of plg> 2 57.-Transverse Section of the gray substance 



of the spinal cord, near the middle of the 



the columns. 2. Nerve cells of various 

 shapes and sizes, with from two to eight 

 processes. 3. Bloodvessels and con- 

 nective tissue. 



Each lateral half of the gray sub- 

 stance is divided into an anterior and 

 posterior horn, and the tractus inter- 

 medio lateralis, or lateral part of the 

 gray substance between the anterior 

 and posterior cornua. 



The posterior horn consists of two 

 parts, the caput cornu, or expanded ex- 

 tremity of the horn (fig. 257), round 

 which is the lighter space or lamina, 

 the gelatinous substance; and the cervix 

 cornu, or remaining narrow portion of 

 the horn, as far forwards as the central 

 canal. 



The gelatinous substance contains 

 along its border a series of large nerve 

 cells ; but more internally consists of a 

 stratum of small cells traversed by 

 transverse, oblique, and longitudinal 

 fibres (figs. 258 and 259). 



dorsal region. Magnified 13 diameters. 



Fig. 258. Transverse Section of the gray substance of the spinal cord through the middle of the 

 lumbar enlargement. On the left side the groups of large cells are seen ; on the right side 

 the course of the fibres without the cells. Magnified 13 diameters. 



Mid? 



Fi.fSUTt 



Nearly the whole inner half of the cervix is occupied by a remarkable and important column 

 of nerve cells, called the posterior vesicular column (fig. 257), which varies in size and appearance 

 in different regions of the cord, and is intimatelv connected with the posterior roots of the 



