672 NEEYOUS SYSTEM. 



tent ourselves with the following very recent description, quoted in full from Gerlacb, 

 which embodies about all of our positive knowledge upon the subject, presented in the 

 clearest manner possible. This extract, the translation of which is almost literal, should 

 be carefully studied by those who desire to learn what is known at the present day 

 with regard to the physiological anatomy of the cord. As a preparation for this study, 

 it would be well to closely examine Fig. 223, which gives a general view of the different 

 parts of the cord, shown in a transverse section : 



" With the present methods and means of investigation at our command, we can 

 scarcely give an exact, detailed description of the course of the fibres in the spinal cord, 

 the groundwork of the physiology of this organ. Investigations up to this time afford 

 at least the outlines of a sketch which, as regards' the course of the fasciculi of the ante- 

 rior roots, has a tolerably definite basis ; and, on the other hand, with regard to the fas- 

 ciculi going to the spinal cord through the posterior roots, is quite incomplete and un- 

 certain. 



" The fasciculi of the anterior roots, after their entrance into the cord, pass diagonally 

 through the white substance, 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 sub- 

 stance to the brain. In consequence of the entrance of additional nerve-fibres, the 

 white substance is necessarily increased in quantity 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 with 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 decussation 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 gelatinosa, dividing into fine and the finest bundles, in the 

 manner mentioned above, to take part in the formation of the vertical bundle of fibres, 

 which lies immediately in front. Here the fibres pass onward, a portion of them ascend- 

 ing and a portion descending. The fibres of the lateral portion of the posterior roots do 

 not remain very long in the vertical bundle, but curve forward in a horizontal plane, 

 and in this way reach the portion of the posterior cornua containing a fine plexus of 

 nerve-fibres. 



" 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 

 curbing, takes here a vertical course to pass into the posterior columns, extending chiefly 

 upward, but perhaps downward as well. The median posterior root-fibres then under- 

 go another deflection, by which they again take a 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 farther course of 

 the posterior root-fibres, it is impossible 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 



