diaphragm

The thoracic diaphragm is a sheet of muscle (shaped somewhat like an open parachute) which extends across the bottom of the rib cage and separates a person’s chest cavity from his/her abdominal cavity. The diaphragm plays an important role in the breathing process because the contraction and relaxation of the diaphragm muscle is what allows air to be drawn into the lungs and then expelled from the lungs.