The simple squamous epithelium that lines the abdominal and pelvic cavities is called the mesothelium; it is derived embryologically from the mesoderm.

The outermost mesothelium, lining the internal surface of the body wall, is the parietal peritoneum. The innermost mesothelium, lining the outer surface of most of the abdominal and pelvic organs, is the visceral peritoneum.

The two layers of peritoneum are continuous with one another at the root of the mesentery, which provides a short attachment to the abdominal wall. The cavity between the two layers of peritoneum is the peritoneal cavity. In the dog the root of the mesentery attaches to the body wall at the level of the second lumbar vertebra. With a few exceptions (e.g. kidneys and ovaries) each abdomi­nal and pelvic organ is linked to the root of the mesentery by folds of mesentery called the mesojejunum, mesocolon, mesorectum, etc. The great mesentery is the collective term for the mesojejunum and mesoileum.

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More on the topic The simple squamous epithelium that lines the abdominal and pelvic cavities is called the mesothelium; it is derived embryologically from the mesoderm.: