The thoracic veins participate in the formation of the left and right venous rings of the heart; they flow into v. cava inferior - the lowest vein of the systemic circulation. The thoracic veins do not have valves.
The thoracic vein has a varying length and can reach the transverse, terminal ribs or the diaphragm. The left cardiac vein (v. aoa - v.a. sinistra cordis) is less long, the right (v.a. dextra cordis) is longer and more tortuous. The superior vena cava (vena cava superior) is not longer than the left cardiac vein, but shorter and wider than it. It begins with two branches - right and left, extending from the corresponding cardiac veins (to the right of the great saphenous vein) behind the base of the body of the sternum and behind the border of the manubrium through the commissure between the anterior border of the bodies of the brachiocephalic trunks, thereby creating the left brachiocephalic trunk - a. subclavia sinistra. Before ascending to the right bronchus, the carina vein is located lateral to the left subclavian trunk. Both veins carry venous blood from the head, neck, mammary glands, upper limb and shoulder, in the elderly - also from the pericardium and posterior mediastinum, located behind the neck of the primary muscle lying along the left shoulder. Part of the blood taken from the lateral sections of the upper half of the body passes through the superior vena cava and neck, rises to the opposite side of the head and then flows to the base of the head and back to the occipital region. After turning to the right, this blood enters the right external and right internal cervical plexus, and from there through the branch of the v.c.s. inflow to v. brachialis (pr.). Some people have v. vertebralis posterior, which receives a branch of the lower semicircle v. basivertebralis. The veins of the head and neck are located in the following order; The venous lymph flow penetrates from the head primarily into the deep cervical lymph nodes that penetrate the neck from the front.