GENERAL PROPERTIES OF THE SPINAL CORD. 673 



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 conditions in the anterior cornua, the following view may be 

 given of the course of the fibres of the posterior roots which penetrate the gray sub- 

 stance : ' A portion of the posterior root-fibres, immediately after their entrance into 

 that portion of the gray substance which contains a nerve-plexus, is lost in this plexus ; 

 another portion extends farther forward, and, in proportion as the fibres pass forward, 

 they likewise take part, by constant divisions, in the formation of the nerve-plexus. This 

 plexus, in which larger and smaller nerve-cells are interspersed as it were as knotted 

 points (Knotenpunkte), is in direct connection with the plexus of the anterior cornua. 

 From these cells nerve-fibres arise, which cross the median line in the gray commissure 

 in front of and behind the central canal, then curve backward to pass up to the brain, in 

 part in the vertical fasciculi of the posterior cornua, in part in the posterior columns, 

 between both of which numerous connections may exist which are as yet inextricable.' 

 This view involves a complete decussation in the spinal cord, through the fibrous elements 

 of the posterior roots passing into this part. Whether this be in reality a complete or a 

 partial decussation in this situation, a part of the fibres arising from the nerve-plexus 

 passing simply backward without crossing the median line, cannot be determined by 

 definite anatomical investigations ; but pathological researches, as well as the experi- 

 mental results of that most competent observer, Brown-Sequard, are decidedly in favor 

 of a complete decussation. 



" Finally, it must be admitted that two points especially are evident : 

 "1. In the direction of the nerve-fibres which enter through the posterior roots, the 

 gray substance has more numerous connections than in those which pass to the spinal 

 cord through the anterior roots. 



" 2. The morphological distinction determinate between the anterior and the pos- 

 terior roots is, that the former take their origin directly from the nerve-cells by means 

 of the nerve-prolongations, while, in the latter, it is only indirect through the nerve-plexus 

 with the protoplasmic prolongations, and in this wise they are in communication with 

 the nerve-cells." 



General Properties of the Spinal Cord. 



In treating of the functions of the spinal cord, we shall consider, first, its general 

 properties, as shown by direct stimulation of its substance in different situations ; next, 

 its functions as a conductor ; and, finally, its action as a nerve-centre. 



The first indication that the different columns of the cord were possessed of different 

 properties is to be found in the experiments of Magendie. This observer, however, was 

 somewhat indefinite in his conclusions, particularly with regard to the anterior columns; 

 but he stated distinctly that the posterior columns are sensitive : " If we lay bare the 

 cord in any portion of its extent, and if we touch, or prick slightly posteriorly, the two 

 fasciculi situated between the posterior roots, the animal gives signs of exquisite sensi- 

 bility ; if, on the other hand, we make the same trials upon the anterior portion, the 

 evidences of sensibility are scarcely apparent." Since this time, numerous observers 

 have experimented upon the different columns, both on the surface and in the deep por- 

 tions of the cord, with varying results. These observations we do not propose to discuss 

 43 



