ABSTRACT
THE ABDOMEN, or abdominal cavity, is the part of the trunk below the diaphragm, which separates it from the thoracic cavity. The lowest part of the abdominal cavity, below the pelvic brim (p. 150), is the pelvic cavity or pelvis. Because of the way the diaphragm bulges upwards into the thorax, the abdominal cavity is larger than might be expected when looking at the outside of the trunk, but lower down it is less capacious than might be expected because of the way the lumbar part of the vertebral column projects forwards in the middle of the posterior abdominal wall. Muscles form the rest of the posterior wall, as they do the anterolateral wall.
