INTERNAL STRUCTURE. ? 



passes in nearly to the centre of the cord (posterior septum"). Its position is marked, 

 especially in the lumbar enlargement and in the cervical region, by a superficial 

 furrow. At its end is the posterior or grey commissure. 



Besides these two median fissures, a lateral furrow is seen on each side of the cord, 

 corresponding with the line of attachment of the posterior roots of the spinal nerves. 

 It is named the postero-lateral groove (fig. 7, C, 4). Each lateral half of the cord is 



Fig. 7. DIFFERENT VIEWS OF A PORTION 



OF THE SPINAL CORD FROM THE 

 CERVICAL REGION WITH THE ROOTS 



OP THE NERVES. Slightly enlarged. 

 (Allen Thomson.) 



In A, the anterior or ventral surface 

 of the specimen is shown, the anterior 

 nerve-root of the right side having been 

 divided ; in B, a view of the right side is 

 given ; in C, the upper surface is shown ; 

 in D, the nerve-roots and ganglion are 

 shown from below. 1, the anterior 

 median fissure ; 2, posterior median 

 fissure ; 3, antero-lateral impression, 

 over which the bundles of the anterior 

 nerve-root are seen to spread (this im- 

 pression is too distinct in the figure) : 4, 

 postero-lateral groove into which the 

 bundles of the posterior root are seen to 

 sink ; 5, anterior root ; 5', in A, the 

 anterior root divided and turned up- 

 wards ; 6, the posterior root, the fibres 

 of which pass into the ganglion, 6' ; 7, 

 the united or compound nerve ; 7', the 

 posterior primary branch, seen in A and 

 D to be derived in part from the ante- 

 rior and in part from the posterior root. 



divided superficially by the postero-lateral groove into a posterior and an antero- 

 lateral part. The attachment of the anterior roots, however, subdivides the latter 

 into anterior and lateral portions. 



An antero-lateral groove has sometimes been described in the line of origin of the anterior 

 roots of the nerves, but usually has no real existence. The fibres of these roots in fact, 

 unlike the posterior, do not dip into the spinal cord in one narrow line, but spread over a 

 space of some breadth. 



On the posterior surface of the cord, at least in the upper part, there is on each 

 side of the middle line a slightly marked longitudinal furrow (fig. 11) situated about 

 one millimeter from the posterior median fissure, and marking off, in the cervical 

 region, a slender tract, the postero-mesial column. This sulcus, which is better 

 marked in some individuals than in others, is termed the posterior intermediate 

 furrow. An incomplete connective tissue septum (posterior intermediate septum) 

 extends from the furrow into the white substance of the cord. The larger remaining 

 part of the posterior column is termed the postero-lateral column. 



INTERNAL STRUCTURE OF THE SPINAL CORD: RELATIVE PROPORTIONS OP GREY 



AND WHITE MATTER. 



Grey matter. When the spinal cord is cut across (figs. 8, 11, 14) it is seen that 

 the grey matter occupies the more central parts, being almost completely enclosed by 

 the white matter. The grey matter appears in the form of two irregularly crescentic 

 portions on either side, united across the middle line by the posterior grey commis- 

 sure before mentioned, so that its section may be compared in shape to the letter H. 



