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

MS, medullary sheath, the dark, irregular ring just inside the bundles.

From Wood and Forest by William Noyes

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 George Herbert Betts

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

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

Each one of the perforations is the entrance to an oblique tunnel, which is bored in the medullary sheath of the twig.

From Social Life in the Insect World by Bernard Miall

It will help in understanding the peripheral system to remember that a nerve consists of a bundle of neurone fibers each wrapped in its medullary sheath and sheath of Schwann.

From The Mind and Its Education by George Herbert Betts