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mesothelium mes·o·the·li·um (měz'ə-thē'lē-əm, měs'-)
n. pl. mes·o·the·li·a (-lē-ə)
The layer of flat cells of mesodermal origin that lines the embryonic body cavity and gives rise to the squamous cells of the peritoneum, pericardium, and pleura.
A layer of flattened epithelial cells that lines the membranes of closed body cavities, including the pericardium, pleurae, and peritoneum. Compare endothelium.