390 OEIGINAL AETICLES. 



longitudinal, sometimes escaping directly to surrounding parts. The 

 cells around the cylinder send off their processes into the anterior 

 and posterior cornua, and contribute to form the commissure behind 

 the central canal. In the inner side of the cervix of the middle of 

 the cervical and lumbar enlargements the cells are larger than in 

 any other region — in man and mammalia they are here reduced in 

 size. These columns do not exist in birds. 



The posterior roots are intimately connected with the vesicular 

 columns, as will be shown farther on. 



Van der Kolk, as already stated, doubts the independent existence 

 of this particular column (p. 37), " As Clarke has correctly stated, 

 several columns of multipolar ganglionic cells extend through the 

 entire length of the spinal cord, those in the anterior being the 

 principal ; next in importance, those at the side of the posterior 

 commissure ; then those in the middle of the grey matter, between 

 the anterior and posterior horns ; and, lastly, those in the posterior 

 horns themselves, as the smallest. These columns, however, are not 

 to be regarded as qiiite independent ; on the contrary, they are all 

 more or less connected." 



A band of fibres from the posterior transverse commissure after 

 curving round the front of the vesicular cylinder, runs longitudinally 

 outwards to the tractus intermedio-lateralis. Between the latter 

 tractus and the caput cornu, fibres descend from the roots of the 

 nerves, and run partly outwards to the lateral column, and partly 

 forward to the anterior cornu passing through the intermediate tract. 

 Near the outer border of the vesicular columns, at the base of the 

 caput, and near the edge of the cervix, the longitudinal fibres are 

 formed iuto thi'ee or more bundles among, and sometimes embraced 

 by, cells and their processes. 



In receding from the middle of the dorsal region towards either 

 extremity of the cord, the posterior cornua gi'aduaUy separate from 

 behind forwards, receiving between them the deep encroaching layers 

 of the posterior columns, until in the middle of the cervical and 

 lumbar enlargements they are joined by a narrow band of the trans- 

 verse commissure, immediately behiud the canal. The posterior 

 vesicular columns simultaneously undergo changes in form, size, and 

 structure. As they approach the cervical enlargement the cylinder 

 or opaque portion of each is gradually reduced in size. Sometimes 

 the cylinder is intersected by fibres of the transverse commissure ; 

 other fibres of the commissure in their passage outwards enclose it, 

 reunite and run backwards through the caput cornu, diverge and 

 traverse the gelatinous substance as posterior roots of nerves. 



At the upper part of the cervical region, near the origin of the 

 third pair of nerves, a darker mass of cells is found at the base of 

 the cervix on its median border, (fig. 3.) It gradually diminishes 

 upwards, and disappears near the first jjair of nerves. 



In descending the cord from the dorsal to the lumbar region, the 

 posterior grey substance undergoes a series of changes nearly similar 



