Final answer:
The external and internal jugular veins converge with the subclavian vein to form the brachiocephalic vein, which then flows into the superior vena cava, draining blood from the body's upper portion into the heart.
Step-by-step explanation:
The external jugular vein is one of a pair of major veins located in the superficial neck region that drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein. When the subclavian vein merges with the internal jugular and external jugular veins, it forms a vessel known as the brachiocephalic vein. This vein then continues on to contribute to the formation of the superior vena cava, which is the large vein that drains blood from the upper part of the body into the heart.
The superior vena cava is an essential component of the circulatory system as it collects oxygen-depleted blood from the body's upper regions and delivers it back to the heart for reoxygenation. It receives contributions from not only the brachiocephalic veins but also the vertebral and internal thoracic veins, efficiently draining the upper thoracic region.