per·i·to·ne·um also per·i·to·nae·um (pĕr′ĭ-tn-ēəm)
n. pl. per·i·to·ne·a also per·i·to·nae·a (-tn-ēə)
The serous membrane that lines the walls of the abdominal cavity and folds inward to enclose the viscera.
[Middle English, from Late Latin peritonaeum, from Greek peritonaion, from peritonaios, stretched across, from peritonos, stretched around : peri-, peri- + teinein, to stretch; see ten- in the Appendix of Indo-European roots.]
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