178 



THE HUMAN BODY. 



the levels of the nerve-roots horizontal white fibres are 

 found (9 and 10, Fig. 74, and a, Fig. 75) running into the 

 gray matter, and others exist at the bottom of the anterior 

 fissure, running from one side of the cord to the other. 

 In the gray substance the same supporting network of con- 

 nective tissue is found, but in it the majority of the nerve- 

 fibres are non-medullated, and at certain points nerve-cells, 



FIG. 74, A thin transverse section of half of the spinal cord magnified about 

 10 diameters. 1, anterior fissure ; 2. posterior fissure ; 3, canalis centralis : 

 8, pia mater enveloping the cord ; 6, 7, bands of pia mater penetrating the cord 

 and supporting its nerve elements ; 9, a posterior root : 10, bundles of an ante- 

 rior root ; a, b, c, d, e, groups of nerve-cells in the gray matter. 



such as are totally absent in the white substance, are found. 

 One collection of these nerve-cells is seen at e in Fig. 74, 

 and others are represented at a, d, /, and elsewhere. The 

 nerve-fibres in the gray matter are for the most part 

 branches of these cells (see Fig. 73), and as they unite 

 with one another freely they form a structurally continuous 



