Peritoneum

The peritoneum is the epithelial[?] lining of the body cavity (coelom). In higher vertebrates, the peritoneum is the lining of the abdominal cavity in particular; the corresponding tissue in the pleural and pericardial cavities of the thorax[?] is called the pleura[?] and the pericardium respectively. The peritoneum is a thin layer of tissue made of flat cells.

A serious medical condition called peritonitis occurs when the peritoneum becomes infected.