Knowledge of the normal structure of the artery wall is necessary to understand the changes of atherosclerosis. The three major layers of arteries, from the innermost out, ne the intima. media, and externa (Figure 3-10A). The intima is a thin layer of connective covered on the inner surface by endothelial cells. The media is primarily smooth muscle. bounded on its inner and outer surfaces by elastic connective tissue. The externa is a connective tissue layer containing tiny blood vessels (vasa vasorum) that nourish the outer half of the arterial wall.