STRUCTUKE OF THE SPINAL COED. 



459 



Fig. 304. 



gray substance, not referable to the roots, and which for the present 

 may be termed special fibres of the spinal cord. 



The gray substance of the cord, in addition to the fibres just de- 

 scribed, contains cells presenting various forms, but all being inva- 

 riably furnished with processes, which, 

 after repeatedly branching, ultimately 

 terminate in extremely fine pale fibrils, 

 like the finest axis-fibres. Kolliker 

 distinguishes three classes of nerve- 

 cells. 1. The cells of the central gray 

 substance (Fig. 304) measure -^Vir to 

 TSOTJ of an inch ; are always pale and 

 granular, with multiple nuclei and 

 branching pale processes. These con- 

 stitute the principal bulk of the cen- 

 tral gray substance. 2. The cells of 

 the substantia gelatinosa resemble the 

 preceding, except that they are of a 

 faint yellowish color, and have one 

 to three processes, and simple nuclei. 

 3. Well-marked cells are seated espe- 

 cially at the apex of the anterior horn 

 (Figs. 279, 280), though also occurring 

 in other portions of the anterior, and 

 in less number in the posterior, horn ; 

 while they are never met with in the substantia gelatinosa and the 

 gray commissure. All these cells are 4^ to 2 J^ of an inch in 

 diameter, with nuclei of 57 V^ to TsV^ f an ^ ncn 5 frequently con- 

 tain brown pigmentary matter, and have from two to nine or even 

 more branched processes, 3^0 IF to 37 \nr f an i nc h i n diameter at 

 their origin. These processes may be traced to a length of T ^ to 

 g\ of an inch, and terminate in fine fibrils, scarcely more than 

 s oiWo f an i n ch thick, all of which are contained within the gray 

 substance. 



Do the nerve-fibres of the roots of the spinal nerves terminate 

 in the white and gray matter of the cord? or do they all ascend to 

 the brain? Yolkmann maintains that they terminate in the cord, 

 and has carried most physiologists with him. We, however, regard 

 Kolliker's reasons for the belief that they proceed to the brain, as 

 far more satisfactory. That the nerve-fibres become attenuated on 

 entering the cord, has already been shown. And the further fact 



Cells from the gray central substance of 

 the cord in man. Magnified 350 diame- 

 ters. (Kolliker.) 



