medullary sheath medullary ray • medulla spinalis · · · Info · Definitions · Synonyms · Characters · · medullary sheath · · Text Common · · Latin · · Scripts 16 · · Length 5 · · Syllables Definitions · · · (noun) a layer of myelin encasing (and insulating) the axons of medullated nerve fibers. Synonyms: medullary sheath, myelin sheath. · · Noun Definition 1 Synonyms · · · myelin sheath · · Synonym 1 Characters · · space U+0020 a latin small letter a U+0061 d latin small letter d U+0064 e latin small letter e U+0065 h latin small letter h U+0068 l latin small letter l U+006C m latin small letter m U+006D r latin small letter r U+0072 s latin small letter s U+0073 t latin small letter t U+0074 u latin small letter u U+0075 y latin small letter y U+0079