The region of the body between the chest and the pelvis. The abdominal cavity is bounded by the ribs and diaphragm above, and by the pelvis below, with the spine and abdominal muscles forming the back, side, and front walls. The abdominal cavity contains the liver, stomach, intestines, spleen, pancreas, and kidneys. In the lower abdomen, enclosed by the pelvis, are the bladder, rectum, and, in women, the uterus and ovaries.
The spine, pelvis, and ribs provide attachments for the layers of muscle that make up the abdominal walls. There is a layer of fat between these muscles and the skin. The inner surface of the abdominal muscles is covered by a thin membrane, the peritoneum, which also covers the organs, such as the pancreas and kidneys, that are fixed to the back wall. Folds of peritoneum also cover the mobile organs, such as the stomach and intestines.