medullary sheath

American  

noun

1. Botany. a narrow zone made up of the innermost layer of woody tissue immediately surrounding the pith in plants.

2. Anatomy. myelin sheath.

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medullary sheath British  

noun

1. anatomy a myelin layer surrounding and insulating certain nerve fibres

2. a layer of thick-walled cells surrounding the pith of the stems of some higher plants

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Etymology

Origin of medullary sheath

First recorded in 1840–50

Example Sentences

The medullary sheath may also aid in the nourishment of the axis cylinder.

From Physiology and Hygiene for Secondary Schools by Walters, Francis M.

The "white matter" of the central system consists chiefly of axons with their enveloping or medullary, sheath and neuroglia.

From The Mind and Its Education by Betts, George Herbert

Axons without the medullary sheath are found in the sympathetic nerves.

From Physiology and Hygiene for Secondary Schools by Walters, Francis M.

Related to this substance are ``neuro-keratin,'' found in the medullary sheath of nerves, and ``gorgonin,'' the matrix of the axial skeleton of the coral Gorgonia Cavolinii.

From The Project Gutenberg Encyclopedia Volume 1 of 28 by Project Gutenberg

In the white masses the medullary sheath is present.

From The Mind and Its Education by Betts, George Herbert