NEEVE-TISSUE. 



297 



assertion is contrary to our ideas of nerve action and so is the assertion of 

 other histologists, that the axis-cylinder is a fluid. 



In peripheral formations of connective tissue f. i., in the 

 female breast, the derma of the skin, etc. we often encounter 

 single medullated nerve-fibers, exhibiting the characteristic feat- 

 ures just described. Their double contour is due to the presence 

 of the myeline sheath, and not to the refraction of the myeline r 

 for the double contour is visible even when the myeline is absent.. 

 The fluted appearance of medullated nerve-fibers is partly due to 



FIG. 126. MEDULLATED NERVE-FIBERS OF THE FEMALE BREAST. 



N, nerve-libers ; C, capillary blood-vessels ; F, fat-globule with vacuoles. Magnified 60G 1 

 diameters. 



the presence of the oblong nuclei in the myeline sheath, and 

 partly to constrictions along the course of the nerve-fiber, to the 

 presence of which Remak, and recently Schmidt, drew attention,, 

 the nature of which is not yet understood. All these features 

 are marked characteristics of medullated nerve-fibers, in contra- 

 distinction to those of capillary blood-vessels. (See Fig. 126.) 



In nerve-bundles no ramification of the fibers takes place, but. 

 as they approach the periphery, either motor or sensitive, they 

 branch very freely, and one fiber often splits into a number 

 of slightly thinned branches. 



