Histology of a small artery (left) and vein. The artery has a moderately thick wall of smooth muscle (tunica media) and shows a partly contracted internal elastic lamina (black). The vein has a thin wall comprised of a layer of smooth muscle and elastin fibres. Tunica adventitia of connective tissue (green) surrounds each vessel. Trichrome stain. Magnification x180 at 10 cm wide.