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 external iliac artery admits of being tied in a surgical operation at any part except near its upper and lower end ; the near neighbourhood of the upper end being excepted on account of the circulation through the internal iliac, and the lower end on account of the common position of the branches (epigastric and circumflex iliac). Occasional deductions from this statement occur in consequence of a branch or branches taking origin near or at the middle of the artery; and as the operator may see such a branch he will avoid placing a ligature very near it.
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The vessel which supplies the lower extremity forms a continuous trunk from the point of division of the common iliac artery down to the lower border of the popliteus muscle, where it divides into the anterior and posterior tibial arteries ; but though thus continued as a single trunk different parts of the vessel have received different names, taken from the anatomical regions through which they pass. Whilst within the pelvis, it is named iliac; in the upper two-thirds of the thigh, femoral ; and thence to its termination, popliteal. These divisions, however, are artificial, and are intended merely to facilitate reference to the vessel in different situations.
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Before escaping from the pelvis, the pudic artery occasionally gives small and irregular branches to the muscles and to the sacral nerves : and, besides its two terminal branches, it furnishes several named branches in the perineum.
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