Muscular artery. Light micrograph of a transverse section through a muscular artery. This blood vessel has a thick, muscular wall that enables it to carry blood under pressure. This wall is composed of three layers. The innermost tunica intima surrounds the lumen (tube, white). It possesses a fine elastic sheet (dark purple, convoluted) known as the internal elastic lamina. The middle layer, the thick tunica media, is mainly composed of smooth muscle fibres (purple), interspersed with a few connective collagen fibres (blue). The external tunica adventitia (blue) is composed mainly of connective tissue. Trichrome blue stain. Magnification unknown.