FIBER TRACTS OF THE SPINAL CORD 



97 



Fasc. gracilis 

 \ Fasc. cuneatus 



part of these ascending branches of the dorsal root fibers, the former contain- 

 ing those which have the longest intramedullary course. 



The descending branches of the fibers of the medial division of the dorsal 

 root are all relatively short. The shortest terminate at once in the gray matter 

 of the posterior column. Others descend in the fasciculus interfascicularis, or 

 comma tract of Schultze, which is situated near the center of the posterior fu- 

 niculus; and still others run near the posterior median septum in the septomar- 

 ginal fasciculus (Fig. 76). In both of these fas- 

 cicles they are intermingled with descending fibers, 

 arising from cells within the gray matter of the spinal 

 cord. 



Collaterals. At intervals along both ascending 

 and descending branches collaterals are given off which 

 run ventrally to end in the gray matter (Fig. 70). 

 They are much finer than the fibers from which they 

 arise, and the total number arising from a given fiber 

 is rather large. Some of them end in the ventral 

 gray column; others, in the posterior gray column, 

 including the substantia gelatinosa and the nucleus 

 dorsalis; still others run through the dorsal com- 

 missure to the opposite side of the cord, where they 

 appear to end in the posterior columns (Fig. 72). In 

 Fig. 70 there are illustrated the arborizations formed 

 by some of these collaterals about cells of the posterior 

 column. 



The terminals of the descending branches and of 

 those ascending branches, which do not reach the brain, 

 end as do the collaterals within the gray matter of the 

 spinal cord. 



The fibers of the lateral division of the dorsal root are all very fine. The 

 majority are unmyelinated and can be recognized only in preparations in which 

 the axons are stained. A good account of their appearance in Golgi prepara- 

 tions has been given by Barker (1899, pp. 466-468). In Weigert preparations 

 we must look carefully to find the few myelinated fibers contained in this divi- 

 sion. But in pyridin-silver preparations great numbers of fine unmyelinated 

 fibers, accompanied by a few which are myelinated, can be seen to turn lateral- 

 ward as the root filament enters the cord. These constitute the lateral division 



Fig. 71. Diagram to 

 illustrate the arrangement 

 of the ascending branches 

 of the dorsal root fibers 

 within the posterior funic- 

 ulus of the spinal cord. 



