The peritoneum is the largest serous membrane in the body. It completely surrounds the body cavity and contains the viscera and other body organs. In males, it is a completely closed sac, but in women, the peritoneum is perforated by the ovaries and fallopian tubes. The peritoneum is divided into two subdivisions, the parietal and visceral. The peritoneal cavity is the space that lies between these two portions of the membrane.

This important membrane has an interesting embryonic development. From early embryonic tissues a whole series of supportive tissues grow to contain and support the internal organs. The peritoneum is multi-layered. The outer layer of the visceral peritoneum forms the serosa of most of the intestinal tract. Other layers emerge into the abdominal cavity and attach to and support the organs including the intestinal tract. These connective and supportive layers are called the mesenteries. These specialized tissues keep the intestines in place and carry blood vessels and nerve tracts to the organs.

The mesenteries are free membranes connected to the entire digestive system. They are composed of flattened endothelium cells. A thin film of serous fluid lubricates the entire surface. This makes it possible for the organs to slide easily against one another within the body cavity as it moves. The outer surface of the peritoneum is attached to the body wall and is called the smooth surface. Organs slide easily along the cavity wall. The wall of the peritoneum reflects inwardly at various points along its wall. These reflections penetrate deeply into the body cavity and enclose the stomach, liver, spleen, and heart. The offshoots of this important membrane form the greater and small omentum that overlie the abdominal (stomach) wall under the linea alba.