Valves
It is provided with two pairs of valves, the lower pair being placed at its entrance into the subclavian vein, the upper in most cases about 4 cm above the clavicle. The portion of vein between the two sets of valves is often dilated, and is termed the sinus.
These valves do not prevent the regurgitation of the blood, or the passage of injection from below upward.
Read more about this topic: External Jugular Vein