<P> Veins are blood vessels that carry blood toward the heart . Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart . In contrast to veins, arteries carry blood away from the heart . </P> <P> Veins are less muscular than arteries and are often closer to the skin . There are valves in most veins to prevent backflow . </P> <P> Veins are present throughout the body as tubes that carry blood back to the heart . Veins are classified in a number of ways, including superficial vs. deep, pulmonary vs. systemic, and large vs. small . </P> <Ul> <Li> Superficial veins are those closer to the surface of the body, and have no corresponding arteries . </Li> <Li> Deep veins are deeper in the body and have corresponding arteries . </Li> <Li> Perforator veins drain from the superficial to the deep veins . These are usually referred to in the lower limbs and feet . </Li> <Li> Communicating veins are veins that directly connect superficial veins to deep veins . </Li> <Li> Pulmonary veins are a set of veins that deliver oxygenated blood from the lungs to the heart . </Li> <Li> Systemic veins drain the tissues of the body and deliver deoxygenated blood to the heart . </Li> </Ul>

Where are veins located in the human body