*phragm, a somewhat fan-shaped muscle that forms the floor of the chest cavity. It takes its origin from the ensiform cartilage, the six or seven lower ribs and their cartilages, and from the upper three or four lumbar vertebræ, that is, from the whole of the internal circumference of the thorax, and is inserted into the central cordiform tendon. It has several large and several small openings for the aorta, the esophagus, the venæ cavæ, the thoracic duct, and various nerves, and its surfaces are covered by serous membranes, by the two pleuræ and the pericardium above and by the peritoneum below. It partially supports the heart and lungs. Convex toward the chest, it becomes flattened in contraction and so increases the capacity of the chest. It aids in all expulsive acts, as sneezing, coughing, laughing, urinating, defecating, vomiting, and childbirth. Hiccough is spasm of the diaphragm.
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Fig. 38.—Interior view of the diaphragm. (Leidy.) 1-3, The three lobes of the central tendon, surrounded by the fleshy fasciculi derived from the inferior margin of the thorax; 4, 5, the crura; 6, 7, the arcuate ligaments; 8, aortic orifice; 9, esophageal orifice; 10, quadrate foramen; 11, psoas muscle; 12, quadrate lumbar muscle.
The arteries of the chest are the intercostal branches
