Source : WordNet®

medulla
     n 1: a white fatty substance that forms a medullary sheath around
          the axis cylinder of some nerve fibers [syn: {myelin}, {myeline}]
     2: 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" [syn: {medulla oblongata}, {bulb}]
     3: the inner part of an organ or structure in plant or animal
        [ant: {cortex}]
     [also: {medullae} (pl)]

medullae
     See {medulla}