1322 A MANUAL OF ANATOMY 



lateral comu of grey matter, and the cells constitute a column, 

 known as the intermedio-lateral tract of Lockhart Clarke, or the 

 dorsal nucleus of Stilling. This tract extends throughout the entire 

 thoracic region of the cord, and for a short distance into the 

 cervical and lumbar enlargements. 



The posterior vesicular cell-column is situated in the mesial part 

 of the cervix of the dorsal cornu of grey matter. The cells con- 

 stitute the posterior vesicular column of Lockhart Clarke, and they 

 are of large size. Clarke's column exists chiefly in the thoracic 

 portion of the cord. 



The cells of the grey matter differ as regards their axons, some having 

 short, and others long, axons. 



The cells with short axons have their axons confined to the grey matter, 

 in which they ramify not far from the parent-cells. They serve to bring 

 contiguous cells into relation with one another. 



The cells with long axons are partly root-cells and partly association-cells, 

 and their axons travel for some distance from the parent-cells. The axons of 

 the root-cells leave the cord in the fibres of the ventral or motor nerve-roots. 

 The axons of the association-cells constitute association-fibres, which are 

 disposed in two ways: (i) Some enter the white matter of the same side of 

 the cord, in which they divide into ascending and descending branches. 

 Eventually they re-enter the grey matter, and terminate in arborizations at 

 some distance from the parent-cells. (2) Other association-fibres cross to 

 the opposite side in the ventral or white commissure. Some of these end in 

 arborizations around the cells of the grey crescent, whilst others enter the 

 white matter, in which they are disposed as on the side from which they have 

 crossed. 



Destination of Axons of Cells of Grey Matter. 



Cells of Ventral Cornu. — (i) Many axons become the axis-cylinder processes 

 of the efferent fibres of the ventral nerve-roots. (2) Other axons constitute 

 association-fibres, which cross to the opposite side in the ventral or white 

 commissure. After crossing, some end in arborizations around the cells of 

 the ventral cornu ; others enter the white matter ; and a few are regarded by 

 some authorities as entering the ventral nerve-roots of the side to which 

 they have crossed. 



Cells of Lateral Cornu. — ^The axons of the cells of the intermedio-lateral 

 tract of Clarke pass to the efferent fibres of the ventral nerve-roots, and they 

 are regarded as furnishing the white rami communicantes of the sympathetic 

 system. 



Cells of Dorsal Cornu. — The axons of the cells of the dorsal comu have 

 various directions: (i) Some pass to the ventral cornu and ventral or white 

 commissure. (2) The axons of the cells of Clarke's column pass to the lateral 

 column, and are usually regarded as entering the dorsal cerebellar and ventro- 

 lateral cerebellar tracts. (3) The axons of the cells of the substantia gela- 

 tinosa of Rolando pass partly to the lateral column, adjacent to the dorsal 

 horn, where they divide into ascending and descending branches, and partly 

 into the posterior marginal bundle of Lissauer. (4) The axons of other cells 

 in the lateral part of the cervix of the dorsal cornu pass to the lateral and 

 ventral cornua, the ventral or white commissure, and the lateral column. 

 (5) The axons of the cells of the caput cornu posterioris pass to the lateral 

 column of the same side, and a few are regarded as passing to the opposite 

 side in the ventral or white commissure. 



Dorsal or Grey Commissure. — This commissure lies at the bottom 

 of the dorsal median fissure. It consists of (i) grey matter, con- 

 taining a few small nerve-cells, and (2) meduUated nerve-fibres. 

 These fibres pass across from one side to the other, and thereafter 



