The aorta, after having passed the diaphragm is thus named. It rests on the bodies of the vertebras, extending from the front of the last dorsal to the fourth lumbar vertebra, a little to the left of the median line, where it usually divides. The anterior surface of the great artery is successively in apposition with the liver, the splenic vein, the pancreas, the third portion of the duodenum, the left renal vein, and the peritoneum. The vena cava lies at its right side, the right crus of the diaphragm being interposed at the upper part of the abdomen ; close to the same side, are the thoracic duct and the azygos vein, which are placed between the aorta and the right crus of the diaphragm. The aorta is surrounded by a mesh of nerves derived from the sympathetic.
The abdominal aorta, [aorta abdominalis, French : aorte abdominale], gives numerous branches, which may be divided into two sets, viz., those which supply the viscera and and those which are distributed to the walls of the abdomen. The former consist of the coeliac artery, the superior mesenteric , the inferieur mesenteric, the capsular, the renal, and the spermatic arteries ; which among the latter are included the phrenic, the lumbar, and the middle sacral arteries. The first three of the visceral branches are single arteries.
The coeliac artery, [a. coeliaca, French : tronc cœliaque] , a short and very thick vessel, arises from the aorta close to the margin of the diaphragm. In the erect position of the body its direction is nearly horizontal forwards, and it is not more than half an inch long.
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