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 superior mesenteric artery (french : artère mésentérique supérieure) arises from the anterior surface of the aorta, on the middle line, at 2 cm below the origin of the coeliac artery, nearly at the level of the disc between the second and third lumbar, vertebras.
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The femoral artery (femoralis s. cruralis ; French: artère fémorale ), is that portion of the artery of the lower limb which lies along the upper two-thirds of the thigh, — its limits being marked, above, by Poupart's ligament, and below, by the opening in the great adductor muscle, after passing through which the artery assumes the name popliteal.
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The dorsal artery of the foot (a. dorsalis pedis), the continuation of the anterior tibial artery, extends from the termination of that vessel at the bend of the ankle, to the posterior end of the first metatarsal space, where it divides into two branches, of which one proceeds forwards in the first interosseous space, whilst the other dips into the sole of the foot, and terminates by inosculating with the plantar arch. This vessel, in its course forwards, rests upon the astragalus, the scaphoid, and internal cuneiform bones and their respective articulations. It lies in the interval between the tendon of the proper extensor of the great toe, and that of the long extensor of the other toes ; and is covered by (besides the integument) the fascia of the foot, and by a layer of dense cellular membrane, which binds it to the parts beneath. Near its end, it is crossed by the innermost tendon of the short extensor of the toes.
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Frequent mention has been made of the anastomoses which exist between the branches of the arteries in the lower limb ; and a general view of them may now be taken in order that some idea may be formed of the important influence which they exert in maintaining the circulation of the limb, when the principal artery is obliterated by an operation, or by disease.
It may be remarked, in the first place, that the more important of these anastomoses occur in the neighbourhood of the principal articulations of the limb.
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The anterior tibial artery, [a. tibialis antica,] placed along the fore part of the leg, is at first deeply seated, but, as it descends, gradually approaches nearer to the surface. It extends from the division of the popliteal artery to the bend of the ankle, whence it is afterwards prolonged to the interval between the first and second metatarsal bones, under the name of dorsal artery of the foot.
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From the facts above-mentioned, concerning the peculiarities of the three arteries which supply the leg and foot, it will be seen that all the deviations from the ordinary arrangement, in regard to their size, display a general principle of compensation, by which deficiencies in one vessel are balanced by an increase in the size of another.
It will also be observed, that, whilst the anterior and posterior tibial arteries have a greater tendency to diminish than to increase in size, the peroneal artery, on the contrary, is the vessel which is the most frequently enlarged. The anterior and posterior tibials, however, occasionally assist each other, especially in the supply of arteries to the toes.
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