The veins in the lower extremities have one amazing feature Do you see these little moving things? These are valves inside the vessel — you cannot find these in arteries or in veins elsewhere. They are located in the lower extremities in order to prevent the backflow of blood under the force of gravity. In this, the valves are helped by the muscles as they push the blood up when contracting ☝🏻 Moreover, the method that managed to capture these "things" is called ultrasound (USG).