The abdomen comprises that part of the body anterior to the spine and erector spinae and quadratus lumborum muscles, and from the diaphragm above to the rim of the pelvis below. The true pelvis is not included. The peritoneal cavity embraces the cavity of the abdomen and also that of the pelvis. An accurate knowledge of the topographical anatomy of the abdomen with its various contained organs is absolutely essential to both the physician and the surgeon for diagnostic purposes, and especially to the latter in carrying out his operative procedures. The surface of the abdomen should be studied with reference to physical diagnosis; its walls, because herniae frequently protrude through them, and because they must be traversed in obtaining access to the structures within; its contents, in order to properly carry out necessary operative measures.