ANATOMY OF THE NERVOUS SYSTEM. 



183 



the gray substance the same supporting network of connec- 

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

 are non-medullated, and at certain points nerve-cells, such as 

 are totally absent in the white substance, are found. One 

 collection of these nerve-cells is seen at c in Fig. 84, and 

 others are represented at a, e,f, and elsewhere. The nerve- 

 fibres in the gray matter are for the most part branches of 

 the axis cylinder processes of these cells (see Fig. 81), and as 

 they unite with one another freely they form a structurally 

 continuous network through the whole gray substance. The 

 fibres of the anterior roots of the spinal nerves enter the gray 

 matter and there most of them soon become continuous with 

 the axis cylinder process of a nerve-cell; the ending of the 

 posterior root-fibres is not quite certain, but they appear to 

 break up and join the gray network, to be by it placed indi- 

 rectly in connection with nerve-cells. In any case the funda- 

 mental fact remains that every nerve-fibre joining the spinal 

 cord is directly or indirectly in continuity with the gray net- 

 work, and so with all the other fibres of all the spinal nerves., 



FIG. 85. A small bit of the section represented in Fig, 84 more magnified, a, a 

 bundle of fibres from an anterior root passing tli rough the white substance on its 

 way to the gray. Towards the right of the figure the nerve-fibres of the anterior 

 column have been omitted so as to render more conspicuous the supporting con- 

 nective tissue, d and e. Elsewhere the nerve-fibres alone are represented ; c, envel- 

 oping pia mater. The neuroglia is not indicated. 



From the sides of the gray substance, fibres continually pass 

 out into the white portion and become medullated ; some of 

 these enter the gray network again at another level and so 

 bring parts of the cord into especially close union, while 

 others pass on into the brain. At the top of the neck, more- 

 over, the gray matter of the cord is continuous with that of 



