"medulla" in the noun sense
1. myelin, myeline, medulla
a white fatty substance that forms a medullary sheath around the axis cylinder of some nerve fibers
2. medulla oblongata, medulla, bulb
lower or hindmost part of the brain continuous with spinal cord (`bulb' is an old term for medulla oblongata
"the medulla oblongata is the most vital part of the brain because it contains centers controlling breathing and heart functioning"
3. medulla
the inner part of an organ or structure in plant or animal
Source: WordNet® (An amazing lexical database of English)
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