658 STRUCTURE OF THE SPINAL CORD [CH. XLV. 



(2.) Postero-lateral column, or column of Burdach. Many of the 

 fibres of this tract, which is also composed of the entering posterior 

 nerve-roots, pass into the grey matter of the cord either immediately on 

 entrance, or in their course upwards. The rest continue upwards to the 

 medulla oblongata, but those from the lower roots pass into the column 

 of G-oll, as just stated ; those from the upper roots continue to travel 

 upwards in the column of Burdach, and end in the grey matter of the 

 nucleus cuneatus in the medulla oblongata. 



(3.) Dorsal or direct cerebellar tract, or tract of Flechsig. This is 

 found in the cervical and thoracic regions of the cord, and is situated 

 between the crossed pyramidal tract and the margin. It degenerates 

 on injury or section of the cord itself, but not on section of the 

 posterior nerve-roots. In other words, its fibres are endogenous, i.e., 

 arise from cells within the grey matter of the cord ; these cells are 

 those of Clarke's eolumn of the same side ; the fibres are large ones. 



(4.) Ventral cerelellar or antero-lateral ascending tract, or tract of 

 Growers. This is situated in front of the crossed pyramidal and direct 

 cerebellar tracts in the lumbar region, while in the thoracic and 

 cervical regions it forms a narrow band at the margin of the cord, 

 curving round even into the anterior column. Its fibres intermingle 

 with those of the antero-lateral descending tract. They originate 

 from the lower cells of Clarke's column of the same side. 



Both of these tracts, as their names indicate, go to the cerebellum, 

 and form parts of one and the same system ; they connect the cells 

 of Clarke's column of the same side with the cerebellum. In the 

 bulb, the system divides ; the greater number of fibres pass to the 

 vermis by the inferior cerebellar peduncle, while a smaller number 

 run up farther, and then return to the vermis by the superior 

 cerebellar peduncle. A certain number of fibres, especially the 

 smaller and more centrally situated ones, end in grey matter in the 

 bulb, pons, and mid-brain. 



(5.) Tract of Lissauer, or posterior marginal zone. This is a small 

 tract of ascending fibres situated at the outer side of the tip of the 

 posterior horn. These are fine fibres from the posterior roots ; they 

 subsequently pass into the posterior cornu. 



Association fibres in the Spinal Cord. 



Some of the short tracts already alluded to as demonstrable in 

 the spinal cord are bundles of association fibres which connect 

 its different levels together. The main difficulty of investi- 

 gating them by the degeneration method has arisen from the 

 fact that they are largely intermingled with, and so are hard to 

 distinguish from, the long tracts which connect brain and cord 

 together. In 1853 Pfliiger stated that reflex irradiation within the 



