618 STRUCTURE OF THE SPINAL CORD [CII. XLII. 



end in the grey matter of the nucleus gracilis of the medulla 

 oblongata. 



(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 Goll, as just stated ; those from the upper roots continue to travel 

 upwards in ihe 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 column of the same side; the fibres are large ones. 



(4.) Ventral cerebellar 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. 



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

 the dorsal cerebellar enters the cerebellum by its lower peduncle, 

 while the ventral cerebellar enters by its superior peduncle. The 

 fibres terminate by arborising around the cells of that part of the 

 cerebellum known as the vermis or middle lobe. V. Gehuchten states 

 that the ventral tract gives off a few fibres that enter the opposite 

 cerebellar hemisphere by its middle peduncle. 



(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 column. 



(6.) A number of association tracts have been differentiated by 

 Flechsig's and Sherrington's method (see next paragraph). 



Association fibres in the Spinal Cord. 



The numerous short tracts already mentioned as demonstrable in the spinal 

 cord are doubtless bundles of association fibres which connect its different levels 

 together. The main difficulty of investigating 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 spinal cord always took place in an 

 upward direction, but Sherrington in his work found many exceptions to this rule, 

 and he sought for the paths which are capable of carrying the impulses down the 

 cord by a very ingenious method. The spinal cord of a dog was completely 

 divided across, and the animal was kept alive for a considerable time afterwards ; 



