An arched muscle separating thoracic cavity (chest region) from the abdominal cavity, located below the lungs, is called the diaphragm. It helps in respiration process. During breathing in the diaphragm flattens while during breathing out the diaphragm relaxes and becomes arched again. The diaphragm also compresses the abdominal cavity when the inhalation of oxygen occurs.
Diaphragm
