THE NERVOUS SYSTEM. 365 



subdividing to any considerable extent into subordinate fasciculi, to the 

 innermost portions of the anterior horns, skirting the anterior columns. 

 In this course they pass through tlic inner group of the many-rayed, 

 large nerve-cells, in perfectly compact bundles, however, and having no 

 connection whatever with the processes of the cells, as may be readily 

 perceived under a strong magnifying power, when the individual nerve- 

 fibres may be traced quite beyond these cells. Now, if these bundles 

 derived from the anterior roots are traced further it will be perceived, 

 in favorable sections, that they extend to the lateral parts of the anterior 

 commissure, continuing to run in the anterior horns, and, that ultimately, 

 forming more or less Avell-marked curves, they are continuous with its 

 fibres, and in fact are disposed in such a way, that the root-fibres of the 

 right side pass into the left anterior column, and those of the left side 

 into the right. Consequently there is established in the white commis- 

 sure a connection of the longitudinal fibres of the anterior columns and 

 of a part of the motor roots, together with a total decussation. 



A large number of the fibres of the motor roots take no part in the 

 above-described decussation, and are wholly unconnected with the 

 anterior fasciculi, — these are the root-fibres which enter the anterior 

 horns the most externally. Forming, for the most part, smaller fasci- 

 culi, or even as separate fibres, and therefore, less easily observable, 

 they run in part directly backwards, and in part arch outwards, but 

 ultimately bend towards the anterior half of the lateral column, where 

 they pass between the outer groups of the large, many-rayed cells of 

 the anterior horns, and then enter the lateral column in a horizontal 

 direction. These transverse fibres now penetrate to various depths 

 (nearly half, or even more) into the lateral column, then curve uptvards, 

 and after running thus a short distance, appear as longitudinal fibres. 

 Consequently, to express the same thing in other words, a second por- 

 tion of the motor roots arises from the anterior half of the lateral column 

 of the same side, and quits the spinal cord ivithout previously undergo- 

 ing any decussation. 



It is, moreover, worthy of remark, that most of the fibres, perhaps 

 all, which join the motor roots from the anterior and lateral columns, 

 undergo considerable changes in their diameter. Those of the anterior 

 column measure; as has been observed before, at their commencement, 

 on the average, 0-002-0-004: of a line, in the anterior commissure 

 scarcely more than 0-003, and in the gray substance hardly more than 

 0'002 of a line ; 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 scarcely more than 0-002 

 of a line. This diminution in size, however, is again succeeded by an 

 increase in thickness, which takes place, in part, within the gray sub- 

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



