364 THE SPINAL CORD, BY J. GERLACH. 



to the brain, previously intercrossing in the Decussatio pyra- 

 midum of the medulla oblongata. 



The posterior roots of the nerves run horizontally, from with- 

 out inwards, towards the middle line in the white substance of 

 the cord, and are already here divided into two groups. The 

 lateral and smaller one maintains its horizontal direction, and, 

 becoming broken up into fine and still finer fasciculi, traverses 

 the substantia gelatinosa to participate in the formation of the 

 vertical fasciculi situated immediately on its anterior aspect, in 

 which the fibres partly ascend and partly descend. The postero- 

 lateral root fibres, however, do not remain very long in these 

 vertical fasciculi, but curve forwards horizontally, and thus 

 gain that portion of the posterior cornua which possesses a 

 fine nerve-fibre plexus. 



The median and larger division of the posterior root fibres 

 applies itself to that part of the posterior columns which 

 bounds the substantia gelatinosa internally and posteriorly ; 

 the fibres here forming a curve, assume a vertical direction ; and 

 having reached the posterior columns, run for a considerable 

 distance upwards, and perhaps also downwards. These median 

 and posterior root fibres then bend once more, and again be- 

 coming horizontal, enter the grey substance of the posterior 

 cornua, partly through the median portion of the substantia 

 gelatinosa, and partly at its inner border. In regard to the 

 further course of the posterior root fibres in the grey substance, 

 no positive statements can be made, because none of the 

 methods of research at present known enable such fibres to be 

 distinguished from those nerve tubules that either ascend to 

 the brain amongst the vertical fasciculi of the posterior coruna, 

 or, passing out from the grey substance into the posterior 

 columns, ascend to the brain. The frequent subdivision which 

 the posterior root fibres immediately undergo on entering the 

 posterior cornua indicates that some of them at least break up 

 into the fine nerve-fibre plexus of the grey substance. In ad- 

 dition to these, however, are numerous fibres running forwards, 

 and others passing more or less sinuously to the median line. 

 The former may perhaps be regarded in part as posterior root 

 fibres which subsequently and more anteriorly enter the nerve- 

 fibre plexus ; the latter, on the other hand, form commissural 



