ORIGIN OF THE SPINAL NERVES. 



19 



centratis. In this gelatinous substance many of the fibres of the posterior com- 

 missure appear to end (see fig. 15, B). There is rather more of the posterior com- 

 missure behind the central canal than in front. The fibres of the posterior part curve 

 backwards on reaching the crescents of grey matter and pass towards the bundles of 

 the posterior roots, whereas the rest diverge at various angles into the crescent. 



The central canal is lined with a layer of ciliated epithelium (iig. 15, A, A'). 

 Each cell is provided with a bunch of cilia on the side which is turned towards the 



SPINAL GANGUON 

 CEL! 



POSTERIOR ROOT 



I . W 



FJBRES/OF .T/XANTEROLPrreRAI- 



ANT, ROQT 



Fig. 16. DIAGRAM TO ILLUSTRATE THE RELATIONS OF THE ENTERING NKRVE-ROOTS, AND THK FIBRES 



OF THE WHITE COLUMNS OF THE SPINAL CORD TO THE NERVE-CELLS IN THB GREY MATTER. (E.A.S.) 



lumen of the canal : the other end of the cell is prolonged into the reticular 

 substance just mentioned, and there becomes lost to view. 



In the adult human subject the lumen of the central canal is not unfrequently 

 obliterated, being filled up by detached cells. 



OKIGIN OF THE SPINAL NERVES. 



The roots of the spinal nerves are attached along the sides of the cord, opposite 

 to the corresponding horns of the grey matter ; the posterior roots entering along a 

 straight line at the postero-lateral groove, and the anterior roots being scattered 

 somewhat irregularly upon the surface (fig. 7, B). 



The anterior roots are seen in a transverse section to pass through the white 

 substance and to enter the grey cornu in several bundles, which have a slight upward 

 inclination, so as to be often cut obliquely if the section be exactly in a transverse 

 plane. Some of the fibres on reaching the grey matter are directly connected with 

 the axis-cylinder processes of the large nerve-cells of the cornu. Others pass by 

 the cells without, so far as can be seen, entering immediately into relation with 

 them. 



As soon as the bundles enter the grey matter, their fibres diverge from one 

 another, some passing mesially, others laterally, and others straight backwards (fig. 16). 

 Of those which pass mesially some are continued into the axis-cylinder processes of 



c 2 



