Me`di·as'tineMe`di*as*ti'num noun [ New Latin mediastinum , from Latin medius middle; confer mediastinus helper, a menial servant, Late Latin mediastinus equiv. to medius : cf French médiastin .] (Anat.) A partition; a septum; specif... Found on http://www.encyclo.co.uk/webster/M/39
The mediastine or mediastinum is the membranous septum of the chest, formed by the duplicature of the pleura under the sternum, and dividing the cavity into two parts. Found on http://www.probertencyclopaedia.com/browse/EM.HTM
• (n.) Alt. of Mediastinum
Me`di·as'tine 
The mediastine or mediastinum is the membranous septum of the chest, formed by the duplicature of the pleura under the sternum, and dividing the cavity into two parts.