THE SPINAL CORD 115 



fibres. The anterior spinal artery is continued along the 

 front ; it is a very slender vessel. 



The nerve-roots. Consist of anterior and posterior bundles, 

 31 pairs (see p. 158). 



The anterior roots are arranged irregularly along the side 

 of the cord ; the posterior roots issue in a straight line along 

 the postero-lateral groove. They are distinguished from the 

 anterior roots by having a ganglion and by their larger size. 



The nerve-roots pass outward to the intervertebral fora- 

 mina, those in the upper part passing almost transversely ; 

 below they pass more obliquely, until in the lower part of 

 the canal their course is vertical. The collected bundles of 

 nerve-roots at the termination of the cord form the cauda 

 equina. 



FISSURES. 



Anterior median fissure : along the anterior surface of the 

 cord in the middle line. Extends into the substance of the 

 cord for about a third of its thickness, but deeper below than 

 in the upper part. Does not reach grey matter. Lined with 

 pia mater. 



Posterior median fissure : not a true fissure, and only con- 

 tains a septum of pia mater. Reaches down to grey matter. 



Lateral fissures : Antero-lateral : not a true fissure, but a 

 line corresponding to origin of anterior nerve-roots. 



Postero-lateral : corresponding to attachment of posterior 

 nerve roots. 



Columns of the cord : 



The cord being divided into two lateral halves by the 

 median fissures, may again be subdivided into anterior, lateral, 

 and posterior columns. 



The posterior and lateral columns are separated by a groove 

 or lateral sulcus, to which the posterior nerve-roots are 

 attached. 



The anterior and lateral columns are separated by the an- 

 terior roots of the nerves. 



The posterior column is subdivided by a groove (only found 

 in the upper part of the cord), a little outside the posterior 

 median fissure, into two columns, the postero-mesial (of Goll) 

 and the postero-lateral (of Burdach). 



STRUCTURE OF THE SPINAL CORD. 



The spinal cord in transverse section consists of white 

 matter externally, and grey matter internally. 



The grey matter : consists of a crescent-shaped portion it) 



82 



