internal membrane
/ɪnˌtəːnl ˈmɛmbreɪn/noun
1 Anatomy. A membrane lining a part of the body, especially a mucous membrane or endothelium. Now rare.
2 Cell Biol. The cell membrane of a plant cell, contained within the cell wall (now rare ); a membrane contained within a cell or organelle.
Origin
Mid 17th century; earliest use found in Alexander Read (1586?–1641). From internal + membrane.