flechsig's systems of conducting fibres. 



633 



Conducting Systems. The whole of the longitudinal fibres of the spinal cord 

 may be arranged systematically in special bundles, according to their function. 



[Methods. The course [of the fibres and their division into so-called systems has been 

 ascertained partly by anatomical and embryological, partly by physiological and patho- 

 logical means. Apart from experimental methods, such as dividing one column of the cord 

 and observing the results, we have the following methods of investigation : (1) Tiirck found 

 that injury or disease of certain parts of the brain was followed by a degeneration downwards, 

 or secondary descending degeneration of certain of the nerve-fibres connected with the seat 

 of injury, i.e., they were separated from their trophic centres and underwent degeneration. 

 (2) P. Schieferdecker found also, after section of the cord, that above and below the level of the 

 section, certain definite tracts of white matter underwent degeneration [thus showing that 

 certain tracts had their trophic centre below ; this constitutes secondary ascending degenera- 

 tion]. [(3) Gudden's Method. He showed, as regards the brain, that excision of a sense- 

 organ in a young growing animal was followed by atrophy of the nerve-fibres and some other 

 parts connected with it. Thus, the optic nerve and anterior corpora quadrigemina atrophy 

 after excision of the eyeball in young rabbits.] (4) Embryological. Flechsig showed that the 

 fibres of the cord [and the brain also] during development became covered with myelin at 

 different periods, those fibres becoming medullated latest which had the longest course. In 

 this way he mapped out the following systems : 



Flechsig's Systems of Fibres. 1. In the anterior column lie (a) the uncrossed, 

 anterior, or direct pyramidal tract [also called the Column of Turck] ; and ex- 

 ternal to it is (b) the anterior ground bundle, 

 or anterior radicular zone (fig. 454). [The 

 direct pyramidal tract varies in siifce, and it 

 generally extends downwards in the cord to 

 about the middle of the ciorsal region, dimin- 

 ishing steadily in its course; so that it Would 

 seem that this tract contains chiefly fibres for 

 the arm. We do not know, exactly, how these 

 fibres end, whether they cross to the opposite 

 side, or remain on the same side, but most prob- 

 ably most of them pass through the anterior 

 commissure to the grey matter of the opposite 

 side.] 



2. In the posterior column he distinguishes 

 (c) Goll's column, or the postero-median (pos- 



Fig. 454 



tero-internal) column; and (d) the funiculus Scheme of the conducting paths in the 



spinal cord at the 3rd dorsal nerve. 

 The black, part is the grey matter^ v, 

 anterior, hw, posterior, root ; a, 

 direct, and#, crossed, pyramidal tracts; 

 b, anterior column ground bundle ; c, 

 Goll's column ; d, postero-external 

 column ; e andj^ mixed lateral paths ; 

 h, direct cerebellar tracts. 



cuneatus, BurdacKs column, or the -posterior 

 radicular zone, or the postero-external column, 



3. In the lateral column are (e) the antero- 

 lateral tract and (/) the lateral mixed 

 paths, or lateral limiting tract, (g) the lateral 

 or crossed pyramidal tract, and (A) the direct 

 cerebellar tract. 



[All the impulses from the central convolutions or motor areas of the cerebrum, by 

 means of which voluntary movements are executed, are conducted by the pyramidal 

 tracts a and g ( 365). The fibres in these tracts descend from the central con- 

 volutions, i.e., the motor areas pass through the white matter of the cerebrum, con- 

 verging like the rays of a fan to the internal capsule, where they lie in the knee 

 and anterior two-thirds of its posterior segment (the fibres for the face at the knee, 

 and behind this in order those for the arm and leg), they then enter the middle-third 

 of the crusta (fig. 502, Py), pass through the pons into the anterior pyramids of the 

 medulla oblongata, where the great mass crosses over to the lateral column of the 

 opposite side of the cord (crossed pyramidal tract), a small part descending in the 

 cord on the same side as the antero-median tract (direct pyramidal tract, a). The 

 crossed pyramidal tract lies external to the posterior half of the grey matter in the 

 lateral column (fig. 454, g), and it extends throughout the length of the cord. In 



