412 



SPECIAL HISTOLOGY 



the medullary substance, -except that, on the average, they are 

 not more than half as thick, or even less (not more than 



Fig. 143. 



OOOOS'") ; fibres, however, also occur of the same 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 grey 

 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 substance, are continued further in the grey 

 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, h), proceed directly backwards and 



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

 cord in Man, x 350 diam. 



