84 



THE ESSENTIALS OF HISTOLOGY. 



The medullary sheath is composed of a highly refracting fatty 

 material, which gives a characteristic dark contour and tubular appear- 



II 



FIG. 97. WHITE OR MEDULLATED 

 NERVE - FIBRES, SHOWING THE 



SINUOUS OUTLINE AND DOUBLE 

 CONTOURS. 



FIG. 98. PORTIONS OP TWO NERVE-FIBRES 

 STAINED WITH OSMIC ACID (FROM A 

 YOUNG RABBIT). (425 diameters.) 



R, a, nodes of Ranvier, with axis-cylinder 

 passing through, a, primitive sheath of 

 the nerve ; c, opposite the middle of the 

 segment, indicates the nucleus and proto- 

 plasm lying between the primitive sheath 

 and the medullary sheath. In A the nodes 

 are wider, and the intersegmental sub- 

 stance more apparent than in B. (Drawn 

 by J. E. Neale.) 



ance to the nerve-fibres. It affords a continuous investment to the- 

 axis -cylinder, except that it is interrupted at regular intervals in the 

 course of the peripheral nerve-fibres, the axis-cylinder at these places 



