| Noun | 1. | peritoneum - a transparent membrane that lines the abdominal cavity in mammals and covers most of the visceramesentery - a double layer of peritoneum that attaches to the back wall of the abdominal cavity and supports the small intestines omentum - a fold of peritoneum supporting the viscera serosa, serous membrane - a thin membrane lining the closed cavities of the body; has two layers with a space between that is filled with serous fluid |