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The outermost part of the ectodermal sheath of myelinated nerve fibers, including the sheath cell nucleus and its cytoplasm but not the concentric myelin-containing lamellae. Multiple nonmyelinated fibers may be contained within a single neurolemma sheath. (Lockard, Desk Reference for Neuroscience, 2d ed)

Sheath of Schwann, a delicate hyaline membrane surrounding the medullary substance of a nerve fiber, or the axis-cylinder in a non-medullated nerve-fiber.

Very delicate membrane enveloping a nerve.

In anat., the delicate fibrous sheath of a nerve.

The fine transparent, and apparently fibrous membrane that surrounds the nerves-to every filament of which it forms a true canal. Robin restricts the term perinevre to the structure that invests the primitive bundles of nerves; and every nervous filament. It differs from the neurilemma, in its ordinary acceptation, which forms a coat of some thickness in the larger nerves, and supports the nutrient vessels, whilst the perinevre exhibits no capillaries.

The sheath of a nerve-fiber; also, the epincurium.

Syn. : sheath of Schwann. 1. The elastic, hyaline, apparently structureless sheath inclosing a nerve fiber. By some authors the term n. is restricted to the peripheral medullated nerves, whereas others describe non-medullated nerves as possessing a n. but without nodes of Ranvier. See also internode of Ranvier, under internode. [Gr.]