Medulla

n.
  1. Marrow; pith; hence, essence.
  2. (Anat.) The marrow of bones; the deep or inner portion of an organ or part; as, the medulla, or medullary substance, of the kidney; specifically, the medula oblongata.
  3. (Bot.) A soft tissue, occupying the center of the stem or branch of a plant; pith.
  4. See medulla oblongata.
    5. Medulla oblongata . (Anat.),
    the posterior part of the brain connected with the spinal cord. It includes all the hindbrain except the cerebellum and pons, and from it a large part of the cranial nerves arise. It controls very largely respiration, circulation, swallowing, and other functions, and is the most vital part of the brain; -- called also bulb of the spinal cord. See Brain.