THE NECK. 181 



branches wHcli pass tlirough tlie supersacral, tlie inferior 

 through the subsacral foramina. In all other regions this 

 union and subsequent separation occurs after the nerves 

 have pierced the dura mater in passing through the inter- 

 vertebral foramina. This arrangement of the nerve-fibres 

 in an oblique direction in the sacral region forms the caudco 

 equina. The spinal cord consists of two hemispheres j^laced 

 side by side, separated superiorly by the superior longitu- 

 dinal fissure, inferiorly by the inferior longitudinal fissure^ 

 the latter is shallower and broader than the former. They 

 are separated by a transverse band connecting the hemi« 

 spheres, termed the commissure, which consists of grey 

 matter Avith white substance on each surface, of which only 

 the superior layer is thick enough to be visible to the naked 

 eye. A transverse section of the cord shows that centrally 

 it presents grey matter arranged like inverted commas in 

 the hemispheres, connected by the grey commissure the 

 convex surface of one to that of the other. Thus the grey- 

 matter presents two cornua in each hemisphere. The superior 

 is the longest and narrowest, and runs upwards and out- 

 wards, reaching the surface of the cord. The inferior is 

 rounded and separated from the surface by a layer of white 

 matter. From the superolateral part of the cord to which 

 the superior cornu approaches the superior nerve -fibres 

 arise from the whole length of the cord, while from the 

 infero-lateral part nearest the inferior cornu the inferior 

 fibres arise. The superior or sensory fibres are divided into 

 sets which converge towards the intervertebral foramina. 

 They pass through the superior openings in the dura mater, 

 have a ganglion in connection with them, and are micro- 

 scopically indistinguishable from the inferior or motor fibres-^ 

 which run from the cord through the inferior row of open- 

 ings in the dura mater to subsequently unite with the supe- 

 rior fibres forming the spinal nerves. By this arrangernent 

 of the nerve-fibres each hemisphere of the cord is divided 

 into a superior, a middle and an inferior column. The 

 spinal nerves at the commencement send fibres or receive 

 fibres from the nearest sympathetic ganglion. In most 

 regions the ganglia of the sympathetic cord are close 

 against the intervertebral foramina, but in the neck the 

 fibres from each nerve unite to form a branch running witb 

 the vertebral artery through the foramina in the transverse 

 processes of the vertebrae to terminate at the inferior cer* 



