n. [ L. ] 1. Marrow; pith; hence, essence. [ Obs. ] Milton. [ 1913 Webster ]

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. [ 1913 Webster ]

3. (Bot.) A soft tissue, occupying the center of the stem or branch of a plant; pith. [ 1913 Webster ]

4. See medulla oblongata. [ PJC ]

Medulla oblongata. [ L., oblong medulla ] (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. [ 1913 Webster ]

a. See Medullary. [ 1913 Webster ]

a. [ L. medullaris, fr. medulla marrow: cf. F. médullaire. ] 1. (Anat.) (a) Pertaining to, consisting of, or resembling, marrow or medulla. (b) Pertaining to the medula oblongata. [ 1913 Webster ]

2. (Bot.) Filled with spongy pith; pithy. [ 1913 Webster ]

Medullary groove (Anat.), a groove, in the epiblast of the vertebrate blastoderm, the edges of which unite, making a tube (the medullary canal) from which the brain and spinal cord are developed. --
Medullary rays (Bot.), the rays of cellular tissue seen in a transverse section of exogenous wood, which pass from the pith to the bark. --
Medullary sheath (Anat.), the layer of white semifluid substance (myelin), between the primitive sheath and axis cylinder of a medullated nerve fiber. [ 1913 Webster ]

a. (Anat.) Furnished with a medulla or marrow, or with a medullary sheath; as, a medullated nerve fiber. [ 1913 Webster ]

a. Not medullated; Specifically: (Anat.) without a medulla or marrow, or without a medullary sheath; as, a nonmedullated nerve fiber. [ 1913 Webster ]