FIG. 631– Diagram of longitudinal sections of medullated nerve fibers. Osmic acid. (See enlarged image)
FIG. 632– Transverse sections of medullated nerve fibers. Osmic acid. (See enlarged image)
FIG. 633– Diagram of medullated nerve fibers stained with osmic acid. X 425. (Schäfer.) R. Nodes of Ranvier. a. Neurolemma. c. Nucleus. (See enlarged image)
The medullary sheath, or white matter of Schwann(Fig. 631), is regarded as being a fatty matter in a fluid state, which insulates and protects the essential part of the nerve—the axis-cylinder. It varies in thickness, in some forming a layer of extreme thinness, so as to be scarcely distinguishable, in others forming about one-half the nerve fiber. The variation in diameter of the nerve fibers (from 2 to 16μ) depends mainly upon the amount of the white substance, though the axis cylinder also varies within certain limits. The medullary sheath undergoes interruptions in its continuity at regular intervals, giving to the fiber the appearance of constriction
