Pronunciation: (mē"dē-a-stī'num), [key]
—pl. -as•ti•naPronunciation: (-a-stī'nu). [key] Anat.
1. a median septum or partition between two parts of an organ, or paired cavities of the body.
2. the partition separating the right and left thoracic cavities, formed of the two inner pleural walls, and, in humans, comprising all the viscera of the thorax except the lungs.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.