STRUCTUKE OF THE WHITE COLUMNS OF THE SPINAL CORD. 331 



THE WHITE SUBSTANCE OF THE SPINAL CORD. 



The white substance of the spinal cord is invested by a 

 layer of connective tissue belonging to the pia mater. This 

 layer remains adherent to the cord after the removal of the 

 pia mater, and in the newly born, and in young children, can be 

 easily torn away in long filaments, by traction from above 

 downwards. This is attributable partly to the circumstance 

 that this layer is directly continuous with the connective tissue 

 of the cord itself, and partly to the fact that the direction of 

 the fibres of the connective tissue removable with the pia mater 

 is principally longitudinal, whilst that which remains adherent 

 to the cord is chiefly circular. These two layers, however, are 

 continuous with each other, and it is upon the closeness of 

 their connection that the greater or less facility of the removal 

 of the pia mater from the cord is dependent.* Both layers of 

 the pia mater penetrate to the bottom of the sulcus longitu- 

 dinalis anterior, that is to say, to the anterior white commissure ; 

 whilst only the deeper layer of the pia mater, which is adhe- 

 rent to the cord, passes in a straight direction in the sulcus 

 longitudinalis posterior, as far as to the posterior grey com- 

 missure. This septum posterius unites the two posterior 

 columns so firmly together that, in the strict sense of the 

 words, we can scarcely admit the existence of a posterior 

 longitudinal sulcus, and the conflicting views on this point 

 may thus be reconciled. 



The septum posterius is, however, not the only process that 

 the connective tissue surrounding the spinal cord gives off 



* How easily this amorphous connective tissue can be sometimes torn 

 through I observed in the body of a Child which was sent to me some 

 years ago, from a neighbouring town, as presenting the extraordinary 

 feature of possessing a spinal cord that did not give origin to any spinal 

 nerves. The vertebral canal was still unopened, but the already removed 

 and well-preserved spinal cord was packed up with it, from which the 

 whole pia mater, and consequently also the nerve roots, had been detached. 

 In this otherwise exceptional instance, the whole spinal cord had been 

 removed from the still perfect vertebral canal by traction from above, 

 leaving the pia mater and the other membranes of the cord, with the 

 roots of the nerves, m situ. 



