- Botany. a narrow zone made up of the innermost layer of woody tissue immediately surrounding the pith in plants.
- Anatomy. myelin sheath.
Origin of medullary sheath
First recorded in 1840–50
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
- anatomy a myelin layer surrounding and insulating certain nerve fibres
- a layer of thick-walled cells surrounding the pith of the stems of some higher plants
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.