366 



SPECIAL HISTOLOGY. 



144 



of which increase has been already stated in numbers ; so that, proceed- 

 ing from the peripheral nerves, we find them gradually diminishing in 



size from their entrance into the cord 

 until they reach the gray substance, 

 and again enlarging from the point 

 where they join the longitudinal ele- 

 ments of the white substance, but not 

 to 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 indication, as elsewhere in the 

 spinal cord. 



The posterior roots of the nerves, as 

 has been already noticed, penetrate, 

 like the anterior, also horizontally, or 

 in a slightly ascending direction, from 

 the sulcus lateralis posterior, through the longitudinal fibres of the white 

 substance as far as the posterior horns. Here they divide into separate, 

 slenderer, or thicker fasciculi (from 0-01-0-02 of a line), (Figs. 141, , 

 144, 5), and continue, each bundle by itself, in a straight course, and 

 without any direct connection with nerve-cells, quite through the sub- 

 stantia gelatinosa into the substantia grisea. In this course they follow 

 two directions. One portion of them bends upwards, in a uniform curve, 

 or nearly at a right angle, proceeds in the most posterior part of the 

 substantia grisea, close in front of the substantia gelatinosa in a longi- 

 tudinal direction, and gradually joins chiefly the posterior column, but 

 in part also the posterior portions of the lateral column, being continued 

 further, as its longitudinal fibres (Figs. 141, r, 144, g}. A second por- 

 tion of the sensitive roots (Figs. 141, , 144), penetrates, always in a 

 fascicular form, between the above-mentioned longitudinal bundles fur- 

 ther forwards, losing itself in the posterior and in the lateral columns, 

 and also entering the gray commissures. In horizontal sections, the 

 former fibres are frequently very distinct, particularly those going off 

 to the posterior columns (Fig. 141, p, q). I have seen them most dis- 

 tinctly in the inferior extremity of the spinal cord, below the lumbar 

 enlargement, where they ran towards the conus medullaris, close up to 



FIG. 144. Vertical section through the cord, midway between the gray cornua and the 

 point of entrance of the roots of the nerves, magnified about 25 diameters : a, posterior 

 column with the sensitive roots, A, traversing it; 6, substantia gelatinosa; c, prolongations of 

 the posterior roots, which bend round in front of the substantia gelatinosa and run longitudi- 

 nally, in order there to join more particularly the posterior column; </, 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 cornua with the large nerve-cells (the spots), and the also 

 horizontal and divided continuations of the motor roots \f } anterior column traversed by the 

 motor roots, i. 



