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medullary sheath

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.


medullary sheath

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
“Collins English Dictionary — Complete & Unabridged” 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word History and Origins

Origin of medullary sheath1

First recorded in 1840–50
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Example Sentences

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

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.

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.

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

The investment of nerve fibers with a protective covering or medullary sheath, consisting of white, fat-like matter.

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