CHAPTEE XXII. 

 The Course of the Fibehs in the Spinal Coed. 



What becomes of these fibers after tbeir entrance through the spinal 

 nerve-roots into the cord? How much farther have they been traced? It is 

 not the form or shape of the particular part of the central nervous system, 

 but rather the relationship between the different parts, and the communica- 

 tion between fiber and fiber, cell and cell, that must be the basis of in- 

 vestigations. 



The anterior root-fibers may be traced backward and slightly upward, 

 as they pass through the anterior radicular zone. Each single root seems 

 spread out over a large extent of the cord. Arrived at the border of the 

 gray matter, the component fibers separate. As to what occurs to them 

 further, there are many and varied opinions. The following statement, 

 based largely on personal investigation, includes the most important of these. 



And first it is to be accepted as settled that certain fibers of the anterior 

 root arrive at the ventral horn-cells, or rather form their axis-cylinder proc- 

 esses (see Fig. 318). Some of them pass over to cells in the opposite anterior 

 horn, by way of the anterior commissure. 



On pathologic grounds, it has long been recognized that, to the cell- 

 centers of the motor-nerves, fibers pass from the cerebral cortex through 

 the cortico-spinal tracts. It is not difiicult to understand that numerous 

 fibrils from the area of the anterior pyramidal tract (direct pyramidal tract), 

 crossing over through the anterior commissure, enter the opposite anterior 

 horn. Most of these fibrils are collaterals from the fibers proper of this 

 pyramidal tract. In the anterior horn they divide up into fine tufts, which 

 arborize around the ganglion-cells. Only in the recent past has the assump- 

 tion of a connection between these cells and the lateral or crossed pyramidal 

 tracts been proved. Here again it is mainly a matter of collaterals which 

 are given off from these tracts and enter directly the ventral horn of the same 

 side, and there form a fine arborization. 



The pyramidal tracts, therefore, are the secondary motor tracts. 

 Through the close contact of their axis-cylinders they enter into relationship 

 with the cells of origin of the primary motor tract. In Fig. 7 this is 

 schematically represented. 



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