270 NEKVOUS SYSTEM. 



and, as such, are not at all concerned in its formation. On 

 the contrary, they pass immediately to the gray substance 

 of the anterior cornua, and, by their prolongations, are in 

 direct connection with the nerve-cells in this situation, which, 

 accordingly, are to be regarded as the elements of origin of 

 the anterior roots in the cord. The protoplasmic processes 

 of these nerve-cells form parts of the fine plexuses of nerve- 

 fibres in the gray substance, from which larger nerve-fibres 

 take their origin. These, extending in two directions, leave 

 the gray substance, to pass up in the white substance to the 

 brain. In consequence of the entrance of additional nerve- 

 fibres, the white substance is necessarily increased in quan- 

 tity in the cord from below upward. "With regard to the 

 course of the fasciculi which pass out of the gray substance 

 of the anterior cornua, these are to be divided into median 

 and lateral. The median fasciculi pass immediately into the 

 anterior white commissure, where they decussate w r ith corre- 

 sponding fasciculi from the opposite side, to pass upward 

 again in the anterior column of the other half of the cord. 

 The lateral fasciculi go to the lateral columns of the same side, 

 in which they pass to the brain, having first undergone de- 

 cussation in the anterior pyramids of the medulla oblongata. 

 " The posterior nerve-roots enter horizontally, running 

 in the white substance of the spinal cord, in a direction from 

 without inward toward the median line, and here divide into 

 two portions. The lateral portion, the smaller, retains the 

 horizontal direction, and passes through the substantia gelati- 

 nosa, dividing into fine and the finest bundles, in the man- 

 ner mentioned above, to take part in the formation of the 

 vertical bundle of fibres which lie immediately in front. 

 Here the fibres pass onward, a portion of them ascending 

 and a portion descending. The fibres of the lateral portion 

 of the posterior roots do not remain very long in the verti- 

 cal bundle, but curve forward in an horizontal plane, and in- 

 this way reach the portion of the posterior cornua containing 

 a fine plexus of nerve-fibres. 



