diaphragm

In mammals, a thin muscular sheet separating the thorax from the abdomen. It is attached by way of the ribs at either side and the breastbone and backbone, and a central tendon. Arching upwards against the heart and lungs, the diaphragm is important in the mechanics of breathing. It contracts at each inhalation, moving downwards to increase the volume of the chest cavity, and relaxes at exhalation.

The diaphragm has three large openings: one for the oesophagus and vagus nerves, one for the aorta, thoracic duct and azygos vein, and one for the inferior vena cava.