Diaphragm

Diaphragm, the structure which divides the cavity of the thorax from that of the abdomen. It forms an arched dome with its concavity downwards, and contraction of the muscular fibres of the diaphragm by reducing the height of the dome increases the capacity of the chest. The diaphragm is thus the chief muscle concerned in inspiration. The diaphragm is attached posteriorly to the lumbar vertebra; by two ligamentous structures known as the pillars of the diaphragm, laterally its fibres take origin from the six lower ribs, and in front it is attached to the ensiform cartilage. Through the diaphragm pass the aorta with the thoracic duct and vena azygos major; the oesophagus, with the pneumogastric nerves, and the vena cava inferior.