Medulla

(me-dul'-ah). A fatty substance or marrow occupying certain cavities. Also the central parts of certain organs, as distinguished from the cortex. See A Iba. M. of Bone, bone-marrow. M. dorsal is. See M. spinal is. M. of Hair, the central portion or core of the hair. M. of Nerve fiber, the myelin or white substance of Schwann. M. oblong at a, the upper enlarged part of the spinal cord, extending from the cord opposite the foramen magnum to the pons Varolii. M., Renal, the substance of the renal pyramids. M. spinal is, M. vertebral is, the spinal cord or marrow; the myelon. Ferrein; series or bundles of parallel tubules extending from the medulla of the kidney into the cortex. 2. Rays of fundamental ti ue that connect the pith with the cortex, and separate the fibrovascular bundles, in the stems of dicotyledons and gymnosperms. M. Sarcoma, a soft, round-celled sarcoma. M. Sheath, 1. the semi-fluid, fatty, white matter between the enveloping sheath and the central axis-cylinder, or e ential part of a nerve. 2. A sheath composed of spiral ducts and wood-cells surrounding the pith, in dicotyledons and gymnosperms. M. Tube, the closing of the medullary groove, forming a closed medullary or neural tube. M. Velum. See Velum .