The abdomen is the lower part of the trunk below the diaphragm. Its walls surround a large cavity called the abdominal cavity. The abdominal cavity is much more extensive than what it appears from the outside. It extends upward deep to the costal margin up to the diaphragm and downward within the bony pelvis. Thus, a considerable part of the abdominal cavity is overlapped by the lower part of the thoracic cage above and by the bony pelvis below. The abdominal cavity is subdivided by the plane of the pelvic inlet into a larger upper part, i.e., the abdominal cavity proper, and a smaller lower part, i.e., the pelvic cavity. Clinically the importance of the abdomen is manifold. To the physician, the physical examination of the patient is never complete until he/she thoroughly examines the abdomen. To the surgeon, the abdomen remains an enigma because in number of cases the cause of abdominal pain and nature of abdominal lump remains inconclusive even after all possible investigations. To summarize, many branches of medicine such as general surgery and gastroenterology are all confined to the abdomen.
