The jugular veins are part of the circulatory drainage system for the head, carrying blood to the lungs for oxygenation. 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 retromandibular and posterior auricular veins from the head converge, within the parotid gland on either side of the mandible or lower jaw. It follows the posterior edge of the masseter muscle of the jaw, and crosses the sternomastoid muscle which runs 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 on 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 is usually inversely proportional in size to the other veins in the neck, and occasionally double their size.