a) Innermost layer. Composed of a single layer of endothelial cells. Some larger arteries also have an internal elastic membrane (elastica interna).
b) Tunica media: The middle layer, consisting mainly of smooth muscle and elastic fibers (run in a circular direction around the lumen).
c) Outer layer, composed of fibrous connective tissue and fat cells. In some larger arteries, the tunica media and tunica externa are separated by an elastic membrane (elastica externa).