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

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.

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.

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

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

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

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

The medullary sheath and the primitive sheath are not, strictly speaking, parts of the nerve cell, but appear to be growths that have formed around it.

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