500 TEXT-BOOK OF PHYSIOLOGY. 



horn (Clark's vesicular column). From this origin the fibers pass obliquely 

 outward to the surface and then directly upward to terminate, as its name 

 implies, in the cerebellum. Decussation of these fibers takes place in the 

 superior vermiform lobe of the cerebellum. When divided this tract degener- 

 ates upward. It is therefore in all probability an afferent tract and of the 

 second order. 



3. The posterior column, comprising that portion between the dorsal 

 roots and the posterior longitudinal fissure, has been subdivided 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 derived from the dorsal roots of the spinal nerves, which 

 cross this column toward the median line in an oblique or horizontal direc- 

 tion. 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 as- 

 sociative in function. 



(b) The postero-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 oblongata. 

 Fibers derived from cells in the gray matter are also contained in this column. 

 This tract is largely afferent in function. 



(c) 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 ascending and de- 

 scending branches, which finally terminate around cells in the posterior 

 horn. 



In addition to the tracts described in foregoing paragraphs a number 

 of small narrow tracts have been discovered in different regions of the spinal 

 cord the functional significance of which, however, has not been determined. 

 Of these may be mentioned: 



1. The antero-lateral tract of Marchi and Lo wen thai, situated at the 

 anterior and inner angle of the anterior column, which degenerates down- 

 ward after removal of one-half of the cerebellum. 



2. The comma tract, a narrow bundle of fibers situated in the anterior 

 portion of the column of Burdach. When it is divided it degenerates down- 

 ward. 



3. The septo-mar ginal tract, an oval-shaped tract situated along the 

 margin of the posterior longitudinal fissure. 



4. The cornu-commissural tract found 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 lumbosacral region. They 



