Artery. Light micrograph of a section through the wall of a healthy muscular artery. The outer tunica adventitia (right frame) contains a diffuse elastic layer called the external elastic lamina (red). Two vasa vasorum (seen in cross-section), blood vessels that supply blood to the artery wall, are seen: an arteriole (lower right) and a venule (upper right). The tunica media contains a thick layer of smooth muscle. The innermost tunica intima is not seen. Muscular arteries are found in the smaller arterial branches. Their muscle controls the volume of blood reaching the tissue they supply. Orcein stain. Magnification unknown.