THE SPIRAL CORD. 



699 



The white substance of the cord consists of medullated nerve-fibres, with 

 blood-vessels and neuroglia. On transverse section of the white substance of the 

 cord a very striking object is presented. It is seen to be studded all over with 

 minute dots, surrounded by a white area, and this again by a dark circle (Fig. 410). 

 This is due to the longitudinal medullated fibres seen on section. The dot is the 

 axis-cylinder, the white area the substance of Schwann. and the dark circle the 

 tubular membrane of the fibres, which seems to consist of several laminae. 

 Externally, the neuroglia is seen to form a delicate connective sheath round the 

 outer surface of the cord immediately beneath the pia mater, from which numerous 



-White matter. 



Septa of 

 connect i 

 (MMO. 



Central canaL 



\ Gray matter. 



Divided nerve- 

 fibre*. 



-^ J 



FIG. 406. Transverse section through the cervical portion of the spinal cord of the calf. Magnified 40 

 diameters. (Klein and Noble Smith.) 



septa pass in to separate the respective bundles of fibres and extend between the 

 individual nerve-fibres, acting as a supporting medium in which they are im- 

 bedded. Thus it will be seen that the greater bulk of the white matter of the 

 cord is made up of longitudinal medullated fibres, which are arranged in groups 

 forming the antero-lateral and posterior columns. 



There are, however, also oblique and transverse fibres in the white substance. 

 These are principally found (1) at the bottom of the anterior median fissure, 

 forming the white commissure, the fibres passing from the gray matter of the 

 anterior horn on one side to the white matter of the anterior column of the oppo- 

 site side ; (2) horizontal or oblique fibres passing from the roots of the nerves into 



