270 THE NERVOUS SYSTEM 



Helweg). — These tracts arise from the anterior and posterior 

 corpora quadrigemina and from the olive. Passing down- 

 wards they cross over and occupy in the cord a small 

 area opposite the outermost point of the anterior horn 

 (3, a). 



4. Vestibulo-spinal or Anterolateral Descending Tract. — 

 Arising in Deiters' nuclens, through which it gains con- 

 nection with the cerebellum, this tract occupies in the 

 cord a marginal position in the anterolateral column (3). 



Short Descending Tracts : — 



5. Comma Tract (5). — The descending branches of 

 posterior root-fibres. 



6. Septo-marginal bundle (5, m). — Mainly proprio-spinal. 



Ascending Tracts : — 



1, Posterior Columns. — These are formed by fibres from 

 the posterior roots. Passing inwards, these fibres first 

 occupy a position adjoining the posterior horn. As they 

 pass upwards they are gradually pushed towards the 

 middle line by fibres coming in at higher levels. In the 

 upper part of the cord the posterior column becomes 

 divided into two parts — a postero-median part (Column of 

 Goll), containing fibres from the lower limb, and a postero- 

 lateral part (Column of Burdach), containing fibres from 

 the upper hmb. These fibres terminate at different levels 

 by entering the grey matter, the largest travelhng into 

 the medulla, w^here the column of Goll arborises around 

 the nucleus gracilis, and the column of Burdach around the 

 nucleus cuneatus. From these nuclei a second relay of 

 fibres takes origin, and decussating in the medulla, forms 

 the median fillet, which ends in the optic thalamus. From 

 the thalamus a third neurone travels to the cerebral 

 cortex. 



The fibres of the posterior column are uncrossed in the 

 cord. 



