The abdomen is that region of the body cavity below the thorax, separated from it by the musculotendinous diaphragm; below by the brim of the true pelvis. The word abdomen is mentioned in The De re medica (De Medicina) of Celsus the earliest and best Latin medical work written about AD 30 in the first century. Celsus, Aulus Cornelius (25BC-AD50)