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"The axis cylinder is in the center. On either side is seen the medullary sheath, represented by dark lines. The primitive sheath, or neurilemma, is on the outside and represented by white lines in which is a nerve corpuscle with an oval nucleus." — Blaisedell, 1904

Portion of a medullated nerve fiber

"The axis cylinder is in the center. On either side is seen the medullary sheath, represented by dark…