222 NERVOUS SYSTEM. [sect. III. 



grey substance is one of the most difficult of microscopical tasks. 

 If we here more especially consider those of the nerve-roots ; it 

 is seen, that the fibres of the anterior or motory roots, after they 

 have passed into the sulcus lateralis anterior, and into the adjoining 

 parts of the anterior and lateral columns, and have penetrated 

 horizontally through the longitudinal fibres of these, extend further 

 in the grey substance of the anterior horn chiefly in two direc- 

 tions. Some fasciculi proceed directly backwards and somewhat 

 inwards in the innermost part of the anterior horns, bordering on 

 the anterior columns. In this course, many of them pass through 

 the inner group of large nerve-cells, without appearing to be con- 

 nected with the processes of the cells, and, still running in the 

 anterior horns, finally arrive at the lateral parts of the anterior 

 commissure ; they are then continued into the fibres of the latter, 

 and, indeed, in such a manner, that the root-fibres of the right 

 side pass into the left anterior columns, those of the left side into 

 the right. In the white commissure, accordingly, a connection of 

 the longitudinal fibres of the anterior columns, and of a part of 

 the motor roots, conjoined with a total decussation, takes place. 



Another part of the fibres of the motor roots, viz., the outer 

 root-fibres entering the anterior horns, have not the slightest 

 connection with the anterior columns. These fibres, which are 

 generally distributed in bundles, or may even separate into in- 

 dividual fibres, and are, consequently, less readily observable, run 

 partly directly backwards, partly in a curved manner outwards, but 

 finally turn to the anterior half of the lateral columns, where they 

 pass through the outer group of the large multi-radiate cells of the 

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

 course. Now, these transverse fibres extend for a variable distance 

 into the lateral columns (to nearly half or more outwards), then 

 turn upwards, and pursue their course further as longitudinal 

 fibres ; in other words, a second part of the motor roots is in con- 

 nection with the anterior half of the lateral column of the same 

 side, and leaves the cord without ever having decussated. . 



Besides these fibres, there exist many others from the motory 

 roots, which, after having entered the grey substance, spread out 

 in this, especially in the direction of the posterior grey horns, and 

 are lost in the inextricable network of fine nerve-fibres, which 

 occurs in nearly every part of the grey substance. 



All fibres of the motor roots become smaller and smaller from 

 their entrance into the cord as far as the grey substance, to in- 

 crease again when they join the longitudinal elements of the 

 medulla, although they never regain their original diameter. 



