Med"ul*la*ry (?), 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.

2. (Bot.) Filled with spongy pith; pithy.

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.