THE SPINAL CORD. 



715 



commissural fibres, which unite the groups of cells in the gray matter with one 

 another ; (b) of fibres which pass across the anterior commissure from the gray 

 matter of the opposite side ; and (<;) horizontal fibres belonging to the anterior roots 

 of the nerves, which pass through it before leaving the cord. 



In the posterior column of the cord there are two tracts. They are marked 

 off from each other by the posterior intermediate furrow on the surface of the cord. 

 The part which has been described previously as the posterior median column 

 pretty nearly corresponds to the one tract, the tract of Goll, and the remainder 

 of the posterior column corresponds to the other, the tract of Burdach. (7) The 

 tract of Groll increases as it ascends, and consists of long, but small, fibres derived 

 from the posterior roots of the spinal nerves, which ascend to the medulla oblon- 

 gata, where they end in the nucleus gracilis. (8) The tract of Burdach consists 

 of shorter, but larger, fibres than the preceding ; they are, however, derived from 

 the same source, the posterior roots ; some ascend only for a short distance in the 

 tract and then enter the gray matter and come into close relationship with the cells 

 of the posterior vesicular column of Clarke ; others incline toward the mesial plane, 

 and, entering Goll's column, can be traced as far as the medulla. In the cervical 



Anterior Anterior 

 Roots Median 



Fissure. 



FIG. 385. Transverse section of the gray substance of the spinal cord through the middle of the lumbar 

 enlargement. On the left side of the figure groups of large cells are seen ; on the right side, the course of the 

 fibres is shown without the cells. Magnified 13 diameters. 



and upper dorsal regions there is contained in the substance of Burdach's column a 

 small strand of fibres, called the descending comma tract. It presents, on trans- 

 verse section, the appearance of a comma, the blunt extremity of which is directed 

 forward. The fibres forming it probably represent in part descending portions of 

 the dorsal nerve-roots, together with descending commissural fibres within the cord 

 itself. A small strand of similar descending fibres is seen, in the lower part of 

 the cord, lying in the inner part of Goll's column. 



The gray substance of the cord occupies its central part in the shape of two 

 crescentic horns, joined together by the gray commissure. Each of these crescents 

 has an anterior or ventral and a posterior or dorsal cornu. 



The posterior horn consists of a slightly narrowed portion, at its base, where 

 it is connected with the rest of the gray substance this is the cervix cornu : from 

 this it gradually expands into the main part of the horn, the caput cornu ; around 



