Arteries have different diameters, small arteries, medium arteries, large arteries and micro arteries, and their structures are basically the same. The inner membrane is usually composed of endothelium, subendothelium and inner elastic membrane, and the inner elastic membrane is wavy, which is the dividing line of the inner and middle membranes. The middle membrane is thick and composed of multiple layers of smooth muscle, which is called muscular artery, and the size of the canal diameter is adjusted by muscle contraction. The outer membrane is composed of loose connective tissue, with small vessels, lymphatic vessels and nerves in the valve.