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CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



nerve, and are mingled in various proportions in the cerebro-spinal nerves. 

 They differ from the preceding chiefly in not possessing the outer layer of 

 medullary substance; their contents being composed exclusively of the axis- 

 cylinder. 



FIG. 88. Transverse Section of the Sciatic Nerve of a Cat, about X 100. It consists 

 of bundles (funiculi) of nerve fibers ensheathed in a fibrous supporting capsule, epineurium, 

 A,- each bundle has a special sheath (not sufficiently marked out from the epineurium in 

 the figure) or perineurium, B, the nerve fibers, Nf; L, lymph spaces; Ar, artery; V, vein; 

 F, fat. Somewhat diagrammatic. (V. D. Harris.) 



The non-medullated nerves are only about one-third to one-half as 

 large as the medullated nerves, they do not exhibit the double contour, and 



FIG. 89. Small Branch of a Motor Nerve of the Frog, near its Termination, Showing 

 Divisions of the Fibers: a, into two; 6, into three. X 350. (Kolliker.) 



