614 



STRUCTURE OF THE SPINAL CORD 



[CH. XLIL 



terminate by arborising directly around the anterior cornual cells, 

 principally of the same side ; others (6) do so with an intermediate 

 cell station in a posterior cornual cell P 2 ; others (7) arborise around 

 the cells of Clarke's column (C) in the thoracic region of the cord, 

 and from these cells fresh axis-cylinders carry up the impulse to the 

 cerebellum in what is called the direct cerebellar tract, while the 

 main fibre (8) may terminate in any of these ways at a higher level 

 in the cord, or above the cord in the medulla oblongata. When we 

 become acquainted with the structure of the medulla oblongata, we 

 shall be able to trace these fibres further. 



In general terms the anterior root-fibres pass out of the grey 

 matter of the anterior horns, and after a short course leave the spinal 

 cord in the anterior spinal nerve-roots. The posterior roots, on the 

 other hand, do not pass to any great extent into the grey matter 

 immediately, but into the white matter on the inner side of the 

 posterior horn ; in other words, they go into the column of Burdach 

 (fig. 449) ; they pass up in this column, but gradually approach the 

 middle line, and are continued upwards to the medulla in the column 

 of Goll; but as they go up they become less numerous, as some 

 terminate in the grey matter of the cord on the way in the manner 

 described. A few fibres of the posterior root, however, travel for a 

 short distance in a small tract on the outer side of the posterior 



horn ; this is called the tract of 



G n Lissauer (fig. 451); the comma 



tract (fig. 450) has been already 

 explained. 



Suppose now one cuts through 

 several posterior roots between 

 the spinal ganglia and the cord, 

 so that the course of degenera- 

 tion may be more readily traced. 

 Immediately below the points of 

 entrance of these nerve-roots, 

 the comma tract will be found 

 degenerated; immediately above, 

 the degenerated fibres will be 

 found in the column of Bur- 

 dach ; higher up in the cord they 

 will be less numerous, and have approached the middle line; the 

 fibres which enter the cord lowest get ultimately nearest the middle 

 line, so that the greater part of the column of Goll is made up of 

 sensory fibres from the legs ; the fibres which enter the cord last, for 

 instance those from the upper limbs and neck, pursue their course in 

 the inner part of the column of Burdach. 



The preceding figure (fig. 449) shows the degeneration in a section 



FIG. 449. Degeneration in column of Goll after 

 section of posterior nerve-roots. 



