The thoracoabdominal diaphragm is a musculotendinous, dome-shaped partition that separates the thoracic and abdominal cavities. The diaphragm develops from four sources: (1) the septum transversum, (2) the dorsal mesentery of esohagus, (3) the pleu-roperitoneal memranes, and (4) meso-derm of the body wall.