364 



SPECIAL HISTOLOGY. 



and those of the substantia gelatinosa, and consequently require no fur- 

 ther description. 



The nerve-fibres of the gray substance are excessively numerous, so 

 much so as to constitute in any case the half of its bulk, if not more, and 

 exhibit the same conditions as those of the medullary substance, except 

 that, on the average, they are not more than half as thick, or even less 

 (not more than 0-0008 of a line) ; fibres, however, also occur of the same 



Fig. 143. 



size as those in the white substance and in the entering roots of the 

 nerves, especially in the anterior horns, though more widely scattered, 

 and principally towards the anterior roots. The investigation of the 

 course of these nerve-fibres in the gray substance is one of the most 

 difficult tasks in microscopy. If we observe, above all, the roots of the 

 peripheral nerves (Figs. 141, 144), it is apparent : 1. that the motor 

 filaments in them, after they have entered the sulcus lateralis anterior, 

 and the contiguous portions of the anterior and lateral columns, and 

 penetrated horizontally between the longitudinal fibres of the white sub- 

 stance, are continued further in the gray substance of the anterior 

 horns, principally in two directions. The fibres of one bundle, and 

 indeed of that which enters the most internally (Fig. 141, A), proceed 

 directly backwards and a little,, in wards, without forming any plexus, or 



FIG. 143. Large nerve-cells with processes from the anterior cornua of the spinal cord 

 in Man ; magnified 350 diameters. 



