384 THE NERVOUS SYSTEM. 



The posterior column, limited by the posterior median fissure inter- 

 nally and by the posterior nerve roots externally, also consists of fibres 

 from two sources namely, first, fibres coming from the inner border 

 of the posterior horn, the origin of which cannot be more precisely 

 determined ; and secondly, fibres coming, through the gray commissure, 

 from the opposite side of the cord. According to Huguenin,* the 

 posterior columns are formed altogether of these two sets of fibres, 

 and do not receive any from the posterior nerve roots. 



Connection of the Nerve Boots with the Spinal Cord. The anterior 

 nerve roots enter the spinal cord in a number of distinct bundles, which 

 pass horizontally backward between the longitudinal fibres of the white 

 substance and reach the gray substance of the anterior horn. Here 

 their fibres spread out in a variety of directions ; some of them passing 

 inward, some outward, and some almost directly backward. The exact 

 termination of these fibres has not been determined, except for a part 

 of their number. All observers are agreed that some of the root fibres 

 are directly connected with large nerve cells in the anterior horn ; 

 and according to Huguenin, each one of the three groups of cells in 

 this situation receives such communicating fibres. A second portion 

 of the anterior root fibres, described by Kolliker, f and accepted by 

 others, after running outward to the external border of the anterior 

 horn, pass into the white substance, and, turning upward, become 

 part of the longitudinal fibres of the lateral column. A third portion 

 still is composed of fibres which run directly backward toward the 

 posterior horn, but whose termination is unknown. 



The fibres of the posterior nerve roots penetrate the cord in one or 

 two principal bundles, and pass immediately to the gray substance of 

 the posterior horn. Here some of them curve inward, assume a trans- 

 verse direction, and cross the median line, in the gray commissure, to 

 the opposite side of the cord. Others become lost in the gray substance 

 of the posterior horn and the base of 'he anterior horn, without its 

 being possible to ascertain their exact destination ; since the connection 

 of nerve fibres with nerve cells is not seen in the posterior horns. 

 Finally, a third portion of these fibres, according to Kolliker, change 

 their direction and become longitudinal, still remaining in the gray 

 substance and continuing their course in this direction for an unknown 

 distance. 



The anterior and posterior nerve roots, accordingly, resemble each 

 other in one respect, namely, that their immediate destination in the cord 

 is the gray substance of the corresponding horns. But the fibres of the 

 anterior root unite with nerve cells in the anterior horn, or join the 

 longitudinal tract of the lateral column ; while those of the posterior 

 root show no direct connection with nerve cells, but partly cross to the 



* Anatomic des Centres Nerveux. Paris, 1879, p. 266. 

 f Elements d'Histologie Huraaine. Paris, 1868, p. 344. 



