DIAPHRAGM (Gr. Scat/pay,aa, a

See also:

• PARTITION

partition)  . The diaphragm or midriff (Anglo-Saxon, mid, middle, hrif, belly) in human anatomy is a large fibro-muscular partition between the cavities of the thorax and abdomen; it is convex toward the thorax, concave toward the abdomen, and consists of a central tendon and a muscular margin . The central tendon(q, fig. r) is trefoil in shape, its leaflets being right, left and anterior; of these the right is the largest and the Left the smallest . The fleshy fibres rise, in front from the back of the xiphoid cartilage of the sternum (d), laterally by six serrations, from the inner surfaces of the lower six ribs, interdigitating with the transversalis, posteriorly from the arcuate ligaments, of which there are five, a pair of external, a pair of internal, and a single median one . The external arcuate ligament (h) stretches from the tip of the twelfth rib (b) to the costal process of the first lumbar vertebra in front of the quadratus lumborum muscle (o), the internal and middle are continuations of the crura which rise from the ventro-lateral aspects of the bodies of the lumbar vertebrae, the right (e) coming from three, the left (f) from two . On reaching the level of the twelfth thoracic vertebra each crus spreads out into a fan-shaped mass of fibres, of which the innermost join their fellows from the opposite crus, in front of the aortic opening (k), to form the middle arcuate . es . ligament; the outer ones (g) arch in front of the psoas muscle (n) to the tip of the costal process of the first lumbar vertebra to form the internal arcuate ligament, while the intermediate ones pass to the central tendon . There are three large openings in the diaphragm; the aortic (k) is behind the middle arcuate ligament and transmits the aorta, the vena azygos major, and the thoracic duct . In the right leaflet is an opening (sometimes called the hiatus quadrotus) for the inferior vena cava and a branch of the right phrenic nerve (m), while in front and a little to the left of the aortic opening is one for the oesophagus and the two pneumo- gastric nerves (1), the left being in front and the right behind . .0 u . ^u .0 u . ^ .^ ...

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