In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. Its latin name is the transversus thoracis. It separates the thoracic cavity (with lung and heart) from the abdominal cavity (with liver, stomach, intestines, etc.). In relaxed state, the diaphragm is shaped like a dome. It is critically important in respiration: in order to draw air into the lungs, the diaphragm contracts, thus enlarging the thoracic cavity. (The muscles between the ribs also participate in this enlargement.) When the diaphragm relaxes, the air is pushed out by the elasticity of the lung and the tissues lining the thoracic cavity.
If the diaphragm is struck, or for other reasons, it may spasm briefly, making breathing difficult. This is called "being winded" or "having the wind knocked out of you". In some martial arts, practitioners are trained to do this.
- Gray's anatomy, muscles of the thorax