384 



DISSECTION OF THE SPINAL CORD. 



gray crescent, it is resolved into three sets of fibres, external, internal, 

 and middle. 



The outer set penetrate into the antero lateral column. 



The inner set pass through the anterior column and across the median 

 fissure to the opposite half of the cord, decussating with like fibres of the 

 opposite side. 



The middle set enter the substance of the crescent, and are lost in it 

 and in the cells of the intermediate tract. 



The posterior root (j) pierces chiefly the posterior column of the cord, 

 and enters the posterior cornu of the crescent : but a few fibres penetrate 

 by the lateral fissure. It terminates in two bundles of fibres. 



One bundle courses round the outer side of the vesicular column, some 

 fibres enclosing, and others entering it ; and a few fibrils escape into the 

 posterior column of the cord, becoming longitudinal. 



The second bundle is prolonged into the crescent and the intermediate 

 tract, as well as into the transverse commissure behind the central canal 

 of the cord. 



INTRASPINAL VESSELS (fig. 127). Arteries supply the cord and its 



Fig. 127. 



Fig. 128. 



INTRASPINAL ARTBKIES IN THE LOINS (Museum 



of University College, London), 

 a. Branch of the lumbar artery. 

 6. Ascending, and c, its descending offset. 



d. Offsets to the body of the vertebra on each 



side. 



e. Central artery formed by offsets from the 



lateral loops. 



INTRASPINAL VEINS IN THB LOINS. 



a. Branch to join a lumbar vein. 



I. Anterior longitudinal vein, one on each 



side. 

 c. Veins from the bodies of the vertebra. 



membranes, and the bodies of the vertebrae. The veins form a remark- 

 able plexus within the canal, but this will not be seen unless the veins have 

 been specially injected. 



The intraspinal arteries (a) are derived from the vessels along the sides 

 and front of the spinal column, viz., from the vertebral and ascending 

 cervical in the neck, from the intercostal in the Back, and from the lum- 

 bar and lateral sacral below. They are distributed after the following 

 plan : 



As each artery enters the spinal canal by the intervertebral foramen, 

 it divides into two branches, upper and lower. From the point of division 

 the branches are directed, one (b} upwards and the other (c) downwards, 



