<anatomy> 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.

Alternative forms: peritonaeum.

Origin: L. Peritoneum, peritonaeum, Gr, fr. To stretch all around or over; around + to stretch.

(01 Mar 1998)