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TEXT-BOOK OF PHYSIOLOGY. 



3. The posterior column, comprising that portion between the 

 dorsal roots and the posterior longitudinal fissure, has been sub- 

 divided into : 



(a) The postero-external tract of Burdach. This tract lies just 

 within the posterior horns. A portion of this tract is composed 

 of ground fibers which, though vertically disposed, have but a short 

 course. They take their origin in cells in the gray matter, and after 

 entering this tract divide into ascending and descending branches, 

 which with their collaterals re-enter the gray matter at different 

 levels. Another portion of this tract is made up of nerve-fibers de- 

 rived from the dorsal roots of the spinal nerves, which cross this 

 column toward the median line in an oblique or horizontal direction. 

 The fibers of the upper portion of this tract terminate around the 

 nucleus cuneatus at the medulla oblongata. When divided, these 

 fibers degenerate for but a short distance. The ground fibers are 

 probably associative in function. 



(b) The postero-median internal tract, or column of Goll. This 

 tract is separated from the former by a septum of connective tissue 

 which is most marked above the eleventh thoracic segment. The 

 fibers which compose this tract are long and derived for the most 

 part from the dorsal roots of the spinal nerves of the same side. This 

 is shown by the fact that division of these roots central to the ganglion 

 is followed by ascending degeneration of the column of Goll as far 

 as the nucleus gracilis in the medulla. Fibers derived from cells 

 in the gray matter are also contained in this column. This tract is 

 afferent in function. 



(c) The septo-marginal tract. This is an oval-shaped tract 

 situated along the margin of the posterior longitudinal fissure. 



(d) The cornu-commissural tract. This is formed along the 

 border of the anterior portion of the posterior column as far forward 

 as the posterior commissure. Both of these tracts are best developed 

 in the lumbo-sacral region. They arise from nerve-cells in the gray 

 matter. They undergo descending degeneration when divided, but 

 not after division of the dorsal roots. 



(e) Lissauer's tract. This tract embraces the tip of the posterior 

 horn and is composed principally of fibers from the dorsal roots of the 

 spinal nerves. After entering the tract the fibers divide into ascend- 

 ing and descending branches, which finally terminate around cells 

 in the posterior horn. 



(/) The comma tract. This is a narrow tract of fibers situated 

 in the anterior portion of the column of Burdach. When divided, 

 its fibers degenerate downward. 



The Relation of the Spinal Nerves to the Spinal Cord. The 

 spinal nerves present near the spinal cord two divisions which from 

 their connection with the anterior or ventral and the posterior or 



