early 15c., from Late Latin peritonaeum, from Greek peritonaion "abdominal membrane," literally "part stretched over," noun use of neuter of peritonaios "stretched over," from peri- "around" (see peri-) + teinein "to stretch" (see tenet). Related: Peritoneal.
The serous sac consisting of mesothelium and a thin layer of irregular connective tissue that lines the abdominal cavity, covers most of the viscera contained therein, and itself forms two cavities, the peritoneal and the omental bursa, which are connected by the epiploic foramen.
The membrane that lines the walls of the abdomen and the pelvis (called the parietal peritoneum) and encloses the abdominal and pelvic organs (called the visceral peritoneum.) The space between the two, the peritoneal cavity, fills with inflammatory cells and pus when the peritoneum becomes infected.