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Webster 1913 Edition
myeline
my′e-lin
,my′e-line
Noun.
 [Gr. 
μυελόσ 
marrow.] (Physiol. Chem.) 
(a) 
A soft white substance constituting the medullary sheaths of nerve fibers, and composed mainly of cholesterin, lecithin, cerebrin, protein, and some fat. 
(b) 
One of a group of phosphorized principles occurring in nerve tissue, both in the brain and nerve fibers.