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

See Examples For:

medullary sheath

This core is surrounded by the white substance of Schwann, or medullary sheath, which gives the nerve its characteristic ivory-white appearance.

From A Practical Physiology by Blaisdell, Albert F.

These, on entering, lose the medullary sheath and separate into a number of branches that penetrate the corpuscle in different directions.

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

Surrounding the axis cylinder is a thick, whitish-looking layer, known as the medullary sheath, and around this is a thin covering, called the primitive sheath, or neurilemma.

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