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Unformatted text preview: muscle fibers are present. The wall consists primarily of a well-developed tunica adventitia. Many veins, especially those in the limbs, have valves, formed from folds of the tunica intima, that prevent the backflow of blood. If these valves fail to close properly, varicose veins may occur. Many regions of the body receive blood supplies from two or more arteries. The points where these arteries merge are called arterial anastomoses. Arterial anastomoses allow tissues to receive blood even after one of the arteries supplying blood has been blocked....
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- Spring '10