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.
Each is directed outwards, so as to form nearly a right angle with the aorta. In consequence of the position of the aorta upon the spine, the right renal artery has to run a somewhat longer course than the left, in order to reach the right kidney. The artery of the right side crosses behind the vena cava, and both are overlapped by the accompanying renal vein. Previously to reaching the concave border of the kidney, each artery divides into four or five branches, the greater number of which usually lie intermediate between the vein in front, and the upper part of the ureter behind. These branches, after having passed deeply into the fissure of the kidney, subdivide and are distributed in the gland, in the manner described in the account of the structure of that organ.
The renal artery furnishes a small branch to the suprarenal capsule, another which ramifies in the cellular membrane and fat behind the kidney, and a third to the ureter.
The renal artery may be represented by two, three, four, or even five branches ; and the greatest difference is found to exist even on opposite sides of the same body, as to the origin of these accessory vessels. As they usually arise in succession from the aorta itself, it would seem as if the deviation is merely a step beyond that in which the single artery divides into branches sooner than usual after its origin. In some cases a renal artery has been seen to proceed from the common iliac ; and in one case, described by Eustachius, from the internal iliac. Portal found in one instance the right and left renal arteries arising by a common trunk from the fore part of the aorta. In another case, one of several arteries arose from the front of the aorta at its bifurcation, or of the left common iliac at its origin.
The branches of the renal artery, instead of entering at the hilus, may reach and penetrate the gland near its upper end, or on its anterior surface. Lastly, cases occur, though very rarely, in which one of the renal arteries is wanting.
From Quain's anatomy.