In vertebrates such as mammals the abdomen (belly) constitutes the part of the body between the thorax (chest) and pelvis. The region enclosed by the abdomen is termed the abdominal cavity. In arthropods it's the most distal section of the body which lies behind the thorax or cephalothorax. Vertebrates In vertebrates, the abdomen is a large cavity enclosed by the abdominal muscles, ventrally and laterally, and by the vertebral column dorsally. Lower ribs can also enclose ventral and lateral wal… (More on Abdomen)