TRACTS OF THE SPINAL CORD. 361 



extrinsic part of the posterior column. Its size is uniform in the 

 upper three-fourths of the cord, where the posterior intermediate 

 furrow separates it from the fasciculus cuneatus. In depth it 

 reaches to the posterior commissure. Its fibers are the ascending 

 branches of the spinal ganglia cells. Arriving at the clava, all 

 the fibers of the fasciculus gracilis arborize and end in the nucleus 

 funiculi gracilis. 



Fasciculus Cuneatus (Ascending Postero-lateral Tract, 

 Burdach's Column). Beginning in the lower thoracic segments 

 (Fig. 102) the fasciculus cuneatus ascends between the entry zone 

 and the fasciculus gracilis to the nucleus funiculi cuneati of the 

 medulla. It acquires new fibers from every spinal nerve above 

 its origin and grows stronger up to the first cervical nerve. In 

 section it is wedge-shaped, being broadest at the surface ; the edge 

 of the wedge touches the junction of the posterior columna and 

 posterior commissure. Its fibers are ascending, and are branches 

 of the axones of spinal ganglia cells, like the fasciculus gracilis. 

 In the nucleus funiculi cuneati all its fibers arborize and terminate 

 (Collier). 



Descending Tracts Derived from Posterior Roots. The 

 descending fibers from the posterior roots of the spinal nerves 

 arrange themselves somewhat roughly into two tracts, a postero- 

 lateral and a postero-medial (Figs. 102 and 103). These descend- 

 ing radicular tracts greatly expand and multiply the terminal 

 relations of the posterior root-fibers. Mingled with them, there 

 are many fibers of the posterior fasciculus proprius. 



The descending postero-medial tract (Figs. 102 and 103) 

 has received various names at different levels. In the cervical 

 and upper nine thoracic segments, it is the comma tract (of 

 Schultze), situated in the fasciculus cuneatus. Its ventral part 

 disappears in the posterior columna above the tenth segment, 

 but the remainder continues down the cord. Shifting its position 

 in a dorso-medial direction, it takes its place beside the median 

 septum and gradually approaches the cord's posterior surface. 

 It continues in that situation to the end of the cord, and is called, 

 in succession, the oval tract (of Flechsig), the septo-marginal 

 tract (of Bruce and Muir), and the median triangular tract 



