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.
This artery [a. mesenterica inf. French : Artère petite mésentérique], much smaller than the superior mesenteric, supplies the left side of the colon, and the greater part of the rectum. It arises from the aorta, between an inch and two inches above the bifurcation of that trunk. The inferior mesenteric artery deviates to the left side in the direction of the left iliac fossa, from which point it descends between the layers of the meso-rectum into the pelvis, and under the name of "superior haemorrhoidal" artery, runs down behind the rectum. It lies at first close to the aorta, on its left side, and then crosses over the left common iliac artery. Its branches are the following : The left colic artery (colica sinistra), is directed to the left side behind the peritoneum, and across the left kidney to reach the descending colon.
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The 'phrenic arteries [a. phrenicas inferiores], are two small vessels which arise from the aorta, on a level with the under surface of the diaphragm. These little arteries are very irregular in their origin. Supposing them to arise separately one from the other (which will be presently seen to be by no means a constant arrangement), most commonly one is derived from the coeliac artery close to its origin, and the other from the aorta on a level with the under surface of the diaphragm. They soon diverge from each other, and passing across the crura of the diaphragm, incline upwards and outwards upon its under surface.
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The spermatic arteries [a.spermaticae], two small and very long vessels, arise from the fore part of the aorta, a little below the renal arteries. In the fetus they are short, as the testes, at an early period of development, are placed immediately beneath the kidneys; but the arteries become gradually lengthened as these organs are moved from the abdomen into the scrotum.
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The hepatic artery, [a. hepatica, french : artère hépatique], which is intermediate in size, at least in the adult, between the coronary and splenic arteries, gives branches to the stomach, the duodenum, and the pancreas, besides supplying the liver and gall-bladder.
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The renal arteries [a. renales s. emulgentes], of large diameter in proportion to the size of the organs which they supply, arise from the sides of the aorta, about half an inch below the superior mesenteric artery, that of the right side somewhat lower down than that of the left.
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The coronary artery of the stomach (coronaria ventriculi ; French : coronaire stomachique), the smallest of the three visceral branches derived from the coeliac artery, inclines upwards, and to the left side, to reach the cardiac orifice of the stomach.
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