THE NERVOUS SYSTEM 1331 



The tracts of the antero-lateral column may be otherwise arranged 

 as follows : 



Ventral or Anterior Colanin. Lateral Column. 



Direct Pyramidal Tract (descending). Crossed Pyramidal Tract (ieicenJmg). 



Anterior Marginal Bundle (Lowen- Dorsal Spino-cerebellar Tract (ascend- 



thal) {descending). »«o)- 



Ventral Part of Ventral Spiao-cere- Ventral Spino-cerebellar Tract (chief 



bellar Traet {ascending). part of) (ascending). 



Prepyramidal Tract (descending). 



The Spino-Thalamic and Spino-Tectal Tracts (ascending) are con- 

 tained in the ventral spino-cerebellar tract. A part of the posterior 

 marginal bundle (Lissauer's tract) lies superficially in the dorsal 

 part of the lateral column, and it has been described in connec- 

 tion with the dorsal column. 



Association-Fibres of Antero-Lateral Column. — The part of the antero- 

 lateral column which is not occupied by the descending and jiscending tracts, 

 is adjacent to the grey matter, and it constitutes the antero-lateral marginal 

 or ground-bundle. It is di\'ided into two parts — anterior and lateral. 



The anterior marginal or ground-bundle of Lowentlial is situated in the 

 ventral column, in front of the ventral coma of grey matter, and has been 

 already described. 



The lateral marginal or ground-bundle (fasiculus lateralis proprius B.) 

 occupies the lateral column, ventral and mesial to the crossed pyramidal 

 tract. 



The portion of the ventro-lateral ground-bundle adjacent to the grey 

 matter, and almost surrounding it, is known as the limiting zone. 



The fibres of the entire antero-lateral ground-bundle are association — or 

 longitudinal commissural fibres, which serve to coimect the grey matter of 

 successive segments of the spinal cord. They are derived from the cells of 

 the grey matter of the same side, and also of the opposite side, the latter 

 crossing in the ventral or white commissure. 



Arteries of the Spinal Canal and Spinal Cord — ^Arteries ol the 

 Spinal Canal. — These vessels enter the spinal canal through the 

 intervertebral and sacral foramina. In the cervical region they 

 are branches of the vertebral and deep cervical arteries; in the 

 thoracic and lumbar regions they are derived from the dorsal 

 branches of the intercostal and Itunbar arteries ; and in the sacral 

 region they come from the lateral sacral arteries. Within the 

 spinal canal each spinal artery divides into three branches, namely, 

 neural or central, and two parietal, anterior and posterior. The 

 neural or central branch pierces the theca of the spinal cord. It 

 supplies the coverings of the cord and the nerv-e-roots, and it 

 anastomoses with the anterior and posterior spinal arteries on the 

 cord. The neural branch is sometimes spoken of as the lateral 

 spinal artery. The anterior parietal branch of each side passes to 

 the back of the body of a vertebra, near the pedicle, and there it 

 divides into two branches, ascending and descending. These 

 anastomose with the adjacent offsets of the contiguous anterior 

 parietal branches, and in this manner a lateral longitudinal anasto- 

 motic chain is formed, which communicates, at frequent intervals, 

 with its fellow of the opposite side by transverse branches. From 

 these transverse branches ascending and descending offsets are 



