The jugular veins are part of the circulatory drainage system for the head, carrying blood to the lungs for resupply with fresh oxygen. The internal jugular vein drains most of the cerebral veins and outer portions of the face, while the external jugular vein drains most of the outer structures of the head, including the scalp and deep portions of the face.
The beginning of the external jugular vein forms where the retro-mandibular and posterior auricular veins from the head converge, within the parotid gland on either side of the mandible (lower jaw). It follows the back edge of the masseter muscle of the jaw, and crosses the sternomastoid muscles, which run down either side of the neck. The external jugular connects at the base of the throat with the internal jugular, through which the blood continues onward to the heart.
A third, smaller jugular, known as the anterior jugular, comes from the front to join the external jugular before it connects to the internal jugular. The external jugular vein occasionally can be as large as double the size of other veins in the neck.