The diaphragm is a dome-shaped muscle separating the chest from the abdomen. It is the main muscle used for breathing and is involved in other functions.
Diaphragm, dome-shaped, muscular and membranous structure that separates the thoracic and abdominal cavities in mammals; it is the principal muscle of respiration.
The diaphragm, located below the lungs, is the major muscle of respiration. It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily.