an'trum, gen. an'tri, pi. an'tra

[G. antron, a cavity.] i. Any nearly closed cavity, particularly one with bony walls, z. The pyloric end of the stomach, partially shut off, during digestion, from the cardiac end, or fundus, by the pre pyloric sphincter, a. au'iis, meatus acusticus extern us. a. cardi'acum, fore stomach. a. mastoid'eum, mastoid a., a. tympani cum [BNA]. a. of High'more, maxillary sinus [BNA]. a. pylor'icum, a bulging of the pyloric end of the stomach wall along the greater curvature when the organ is distended; see antrum (2). a. tympan'icum [BNA], tympanic a., mastoid a., a cavity in the mastoid portion of the temporal bone, communicating through the mastoid, or posterior, wall of the tympamun with the upper part of this cavity, the attic or epitympanum, and communicating also with the separate mastoid cells.