Peritoneum.—The peritoneum is a serous membrane which lines the walls of the abdominal cavity and invests nearly all its viscera. The kidneys and ureters are outside the peritoneum. The part which lines the walls is called parietal, that which is reflected on the organs visceral, peritoneum. It facilitates the movements of the digestive organs by affording a smooth lubricated surface upon which they can glide on one another. A fold of the peritoneum which connects the stomach with other viscera is called omentum ; a fold which connects the intestinal tube with the posterior walls of the abdomen is called the mesentery ; folds which connect viscera which are not parts of the intestinal canal to the walls of the abdomen, or viscera of any kind to the diaphragm, are called ligaments.

The great omentum, also called gastro-colic omentum, is the largest fold. It invests the stomach and connects it with the transverse colon ; it hangs down from the stomach over the coils of the small intestines like an apron.

The small or gastro-hepatic omentum is a fold which connects the stomach with the liver.

The gastro-splenic omentum is a fold which connects the stomach with the spleen.

The mesentery proper is in connection with the small intestines attaching it to the wall of the abdomen, and enclosing the bloodvessels and nerves.

The mesenteries of the large intestine are the transverse mesocolon, sigmoid mesocolon, and the mesorectum.