634 SECONDARY DEGENERATION OF TROPHIC CENTRES. 



the greater part of its course, it is separated from the surface by the direct cerebellar 

 tract, but where the latter lies further forward, as at the third cervical segment and 

 lower dorsal region, its posterior surface reaches the surface, while from the last dorsal 

 segment, throughout the lumbar region, it comes quite to the surface, as the direct 

 cerebellar tract ceases at the first lumbar vertebra. The pyramidal tract diminishes 

 from above downwards, and its fibres pass into the grey matter of the anterior 

 cornu, and in all probability they subdivide to form fine fibrils, which become con- 

 nected with the dense plexus of fine fibrils produced by the subdivision of the 

 processes of the multipolar nerve-cells. From each multipolar nerve-cell, a nerve- 

 fibre proceeds and passes into the anterior root. The direct cerebellar tract (h) 

 begins about the first lumbar nerve, and increases somewhat in thickness from 

 below upwards, but most of its fibres enter it at the first lumbar and lowest dorsal 

 nerves. It forms a thin layer on the surface of the cord. Its fibres very probably 

 arise in the cells of Clarke's column. As Clarke's column is connected with some 

 of the fibres of the posterior root (for the trunk of the body), it follows that this tract 

 connects certain parts of the posterior roots with the cerebellum. The fibres pass 

 up through the cord and restiform body to the cerebellum. When it is divided, it 

 degenerates upwards, so that it conducts impulses in a centripetal direction.] The 

 anterior (e) and lateral paths (/) and the anterior ground bundle (6) represent the 

 channels which connect the grey matter of the spinal cord and that of the medulla 

 oblongata ; they represent the channels for reflex effects, and they also contain 

 those fibres which are the direct continuation of the anterior spinal nerve-roots, 

 which enter the cord at different levels and penetrate into the grey matter. In e 

 and / there are some sensory paths. Lastly, c unites the posterior roots with the 

 grey nuclei of the funiculi graciles of the medulla oblongata ; d connects some of 

 the posterior nerve-roots through the restiform body with the vermiform process of 

 the cerebellum (Flecksig). The direction of conduction in the posterior columns, 

 which are continuations of some of the fibres of the posterior roots, is upwards, as 

 part of them degenerates upwards after section of the posterior root. Of the fibres 

 of each posterior root, some pass directly into the posterior horn, another part 

 ascends in the posterior column of the same side, and gradually as it ascends, it 

 comes nearer the posterior median fissure. Some of these fibres enter the grey 

 matter of the posterior horn at a higher level. The fibres of the posterior columns 

 run upwards as far as the interolivary layer and the decussation of the pyramids, 

 where they seem to end, or at least form connections with the nerve-cells of the 

 funiculi graciles [clava] and cuneati [triangular nucleus]. A small part as arcuate 

 fibres join the restiform body, and thus the cerebellum is connected with the 

 posterior columns. 



Further, the transverse sectional area of the direct and crossed pyramidal tracts (a and g), 

 the lateral cerebellar tract (h), and Coil's column (c) gradually diminish from above downwards; 

 they serve to connect intracranial central parts with the ganglionic centres distributed along 

 the 8i)inal cord. The anterior root bundle (6), the funiculus cuneatus (d), and the anterior 

 mixed lateral tracts (e) vary in diameter at different parts of the cord, corresponding to the 

 number of nerve-roots. It has been concluded from this that these tracts serve to connect the 

 grey matter at different levels in the cord with each other, and ultimately with the medulla 

 oblongata, so that they do not pass directly to the higher parts of the brain (fig. 443). 



Nutritive Centres of the Conducting Paths. Turck observed that the 

 destruction of certain parts of the brain caused a secondary degeneration of certain 

 parts of the cord, corresponding to the parts called pyramidal tracts by Fleschig 

 (fig. 455). P. Schieferdecker found the same effects below where he divided the 

 spinal cord in a dog. Hence, it is concluded that the nutritive or trophic centre of 

 the pyramidal tracts lies in the cerebrum. [Section of the cord, or an injury com- 

 pressing the cord, besides giving rise to loss of certain functions (p. 648), results 

 in structural changes in certain limited areas of the cord itself. Below the section 



