306 LECTURE XIII. 



within outwardly, split up into a series of groups or seg- 

 ments chiefly following a radiating arrangement, or in 

 some sort into wedge-shapes lobules, in consequence of a 

 sometimes smaller, sometimes larger quantity of connec- 

 tive tissue with vessels pushing its way in between the 

 separate divisions, which are of a fascicular nature like 

 those of the peripheral nerves. This connective tissue is 

 directly connected with the more abundant mass of it 

 present in the grey matter. Now with regard to the 

 nerve-fibres themselves, it is probable that a certain num- 

 ber of them proceed throughout the whole length of the 

 spinal marrow, but it ought certainly not to be assumed 

 that they are all derived from the brain ; a probably 

 considerable portion no doubt have their origin in the 

 ganglion-cells of the spinal marrow itself, and then bend 

 round into the anterior or posterior columns. Besides, 

 the conviction has more and more gained ground, that, 

 both between the two halves of the spinal marrow and 

 between the separate groups of ganglion-cells, direct 

 communications, commissures, exist fibres passing across 

 from one cell to another and from one side to the other, 

 some so as to cross with those of the opposite side (ante- 

 rior commissure), and some so as to run in a straight and 

 parallel direction (posterior commissure). 



With the help of these anatomical observations a no- 

 tion, though indeed as yet a very unsatisfactory one, can 

 be formed of the routes along which the different pro- 

 cesses are carried on within the nervous centres. Every 

 special function possesses its special elementary, cellular 

 organs ; every mode of conduction finds paths distinctly 

 traced out for it. In general too, well-defined peculiari- 

 ties in the structure of the individual nervous centres 

 correspond to the differences of function, and particularly 

 the posterior horns become gradually more and more 

 strongly developed as we ascend ; and in proportion as 



