peritoneum

n. serous membrane lining the abdominal cavity (Anatomy)

In higher vertebrates, the peritoneum is the serous membrane that forms the lining of the abdominal cavity - it covers most of the intra-abdominal organs. It is composed of a layer of mesothelium supported by a thin layer of connective tissue.The peritoneum both supports the abdominal organs and serves as a conduit for their blood and lymph vessels and nerves.
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Peritoneum /peri·to·ne·um/ the serous membrane lining the walls of the abdominal and pelvic cavities and investing the contained viscera, the two [more]Peritoneum - Community and Resources

Noun
1. a transparent membrane that lines the abdominal cavity in mammals and covers most of the viscera
(hypernym) serous membrane, serosa
(hyponym) mesentery

(n.)
The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.