myelin sheath vs medullary sheath

myelin sheath and medullary sheath both are nouns.

Word	Noun	Adjective	Verb	Adverb
myelin sheath	Yes	No	No	No
medullary sheath	Yes	No	No	No

As nouns, myelin sheath and medullary sheath are synonyms defined as:

myelin sheath and medullary sheath: a layer of myelin encasing (and insulating) the axons of medullated nerve fibers

myelin sheath (noun)	medullary sheath (noun)
a layer of myelin encasing (and insulating) the axons of medullated nerve fibers	a layer of myelin encasing (and insulating) the axons of medullated nerve fibers