Medulla - Definition

n 1: a white fatty substance that forms a medullary sheath
around the axis cylinder of some nerve fibers [syn:
myelin, myeline, medulla]
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, medulla, bulb]
3: the inner part of an organ or structure in plant or animal
[ant: cortex]