Medullary

[Sarah]

Filled with spongy pith; pithy. Medullary groove (Anat.), agroove, in the epiblast of the vertebrate blastoderm, the edges ofwhich unite, making a tube (the medullary canal) from which the brainand spinal cord are developed.-- Medullary rays (Bot.), the rays of cellular tissue seen in atransverse section of exogenous wood, which pass from the pith to thebark.-- Medullary sheath (Anat.), the layer of white semifluid substance(myelin), between the primitive sheath and axis cylinder of amedullated nerve fiber.