414 SPECIAL HISTOLOGY. 



lateral columns, undergo considerable changes in their diameter. 

 Those of the anterior columns measure, as has been observed 

 before, at their commencement, on the average, 0*002 — 0-004'", 

 in the anterior commissure scarcely more than 0-003'", and in the 

 grey substance hardly more than 0-002'"; and the same is the 

 case also with those of the lateral columns ; which, however, even 

 while still in the interior of the column, where their direction is 

 horizontal, measure scarcelv more than 0-002'". This diminution 

 in size, however, is again succeeded by an increase in thick- 

 ness, which takes place, in part, within the grey substance, 

 in part at the point where the radical bundles quit it, the 

 amount of which increase has been already stated in numbers: 

 so that, proceeding from the peripheral nerves, we find them 

 gradually diminishing in size from their entrance into the 

 cord until they reach the grey substance, and again enlarging 



from the point where they join 

 the longitudinal elements of the 

 white substance, but not to 

 ff- --, j such an extent as ever to attain, 



nearly their pristine diameter. 

 Of divisions in the fibres of the 

 anterior roots in the anterior 

 horns, I have seen as little in- 

 g-'J' : dication, as elsewhere in the 



spinal cord. 

 ^£§§§ 3S The posterior roots of the 



/' / iv^'^xffVf nerves, as has been already 



4 Hf^ noticed, penetrate, like the an- 



terior, also horizontally, or in 

 j fa . 



a slightly ascending direction, 



from the sulcus lateralis posterior, through the longitudinal 

 fibres of the white substance as far as the posterior horns. 



Fig. 144. Vertical section through the cord, midway between the grey cornua 

 and the point of entrance of the roots of the nerves, x about 25 diam.: a, posterior 

 column with the sensitive roots, h, traversing it ; b, substantia gelatinosa ; c, pro- 

 longations of the posterior roots, which bend round in front of the substantia 

 gelatinosa and run longitudinally, in order there to join more particularly the posterior 

 column ; d, basis of the posterior cornua, with the ends of the horizontal portion of 

 the sensitive roots apparent (owing to their being cut across) : e, anterior cornu with 

 the large nerve-cells (the spots), and the also horizontal and divided continuations of 

 the motor roots; /, anterior column traversed by the motor roots, /'. 



