676 A MANUAL OF PHYSIOLOGY 



column of Goll ; the outer half the postero-external column, 

 or column of Burdach (Fig. 239). No localization of any 

 of the other conducting paths in the cord is possible by 

 anatomical examination ; but by means of the develop- 

 mental method and the method of degeneration the columns 

 of Goll and Burdach can be followed throughout the cord, 

 and several similar areas can be mapped out. We shall only 

 mention those that are physiologically the most important. 



When the spinal cord is divided, and the animal allowed 

 to survive for a time, certain tracts are picked out by the 

 degeneration of their fibres, although in every degenerated 

 tract some fibres remain unaffected. We may distinguish 

 the tracts that degenerate above the lesion (ascending de- 

 generation) from those that degenerate below the lesion 

 (descending degeneration) . 



Ascending Tracts. Above the lesion degeneration is found 

 both in the posterior and the antero-lateral columns. Imme- 

 diately above the section nearly the whole of the posterior 

 column is involved. Higher up the degeneration clears away 

 from Burdach's tract, and, shifting inwards, comes to occupy 

 a position in the column of Goll. In the antero-lateral 

 column two degenerated regions are seen, both at the 

 surface of the cord, one a compact, sickle-shaped area 

 extending forwards from the neighbourhood of the line of 

 entrance of the posterior roots, and the other an area of 

 scattered degeneration, embracing many intact fibres, and 

 completing the outer boundary of the column almost to the 

 anterior median fissure. The compact area is called the dorsal 

 or direct cerebellar tract, the diffuse area the antero-lateral 

 ascending tract, or tract of Gowers, or ventral cerebellar tract. 



Descending Tracts. When the cord is divided, say in the 

 upper dorsal or cervical region, the following tracts de- 

 generate below the lesion : 



(i) A small group of fibres close to the antero-median 

 fissure, which has received the name of the direct pyramidal 

 tract pyramidal, because higher up in the medulla oblongata 

 it forms part of the pyramid ; direct, because it does not 

 cross over at the decussation of the pyramids, but continues 

 down on the same side 



