Hemidiaphragm: Half of the diaphragm, the muscle that separates the chest cavity from the abdomen and that serves as the main muscle of respiration. Both hemidiaphragms are visible on X-ray studies from the front or back.
The right hemidiaphragm is protected by the liver and is stronger than the left. The left hemidiaphragm is more often subject to rupture and hernia than the right. This may also reflect weaknesses at the points of embryologic fusion of the left hemidiaphragm.
See also: Elevated hemidiaphragm.