AX ATOMY OF THE SPIXAL CORD. 271 



" The median (larger) portion of the posterior root-fibres 

 passes to that portion of the posterior, column which bounds 

 the substantia gelatinosa internally and posteriorly ; and 

 curving, takes here a vertical course to pass into the poste- 

 rior columns, extending chiefly upward, but perhaps down- 

 ward as well. The median posterior root-fibres then undergo 

 another deflection, by which they again take an horizontal 

 direction, and pass to the gray substance of the posterior 

 cornua, in part through the median portion and in part by 

 the inner border of the substantia gelatinosa. With regard 

 to the further course of the posterior root-fibres, it is impos- 

 sible to present positive explanations, for the reason that the 

 present methods of investigation do not afford any means of 

 distinguishing the posterior fibres from the nerve-tubes in 

 the vertical fasciculi of the posterior cornua, or those passing 

 from the gray substance into the posterior columns, to ascend 

 to the brain. The numerous divisions which the posterior 

 root-fibres penetrating the posterior cornua immediately 

 undergo indicate, however, that a portion of them is lost 

 directly in the fine nerve-plexus of the gray substance. But 

 at the same time there are numerous fibres which extend 

 forward, and others which take a more or less wavy course 

 toward the median line. The first, perhaps, can be regarded 

 as posterior root-fibres, which pass in a forward direction in 

 the nervous plexus ; the latter, on the other hand, belong to 

 the commissural fibres, which cross the median line in the 

 gray substance in front of and behind, the central canal. In 

 my opinion, the fibres which penetrate the posterior com- 

 missure are not to be regarded as belonging directly to the 

 posterior roots, but are to be considered as fibres which pass 

 backward to go either to the vertical fasciculi of the gray 

 substance, or to pass to the brain in the posterior columns. 

 If this idea be correct, and it is sustained by analogous con- 

 ditions in the anterior cornua, the following view may be 

 given of the course of the fibres of the posterior roots which 

 penetrate the gray substance : ' A portion of the posterior 



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