The brachiocephalic veins are formed behind the sternoclavicular joints by confluence of the internal jugular and subclavian veins. It should be noted that each internal jugular vein lies lateral to the common carotid artery, in front of scalenus anterior muscle. The subclavian vein, running medially into the brachiocephalic, lies lateral to and then below the muscle. Medial to scalenus anterior, in front of the first part of the subclavian artery, the vein has been joined by the internal jugular vein and is thence called the brachiocephalic. This part of each brachiocephalic vein receives tributaries corresponding to the branches of the first part of the subclavian artery (vertebral, inferior thyroid, internal thoracic and, on the left side only, superior intercostal).
The right brachiocephalic vein commences behind the right sternoclavicular joint and runs vertically down¬wards. It receives the right lymphatic duct and right jugular and subclavian lymph trunks, which normally enter independently of each other.
The left brachiocephalic vein passes almost horizontally across the superior mediastinum to join the right vein at the lower border of the first right costal cartilage. In the infant the left brachio¬cephalic vein projects slightly above the jugular notch, and may do so in the adult if the vein is distended, especially if the head and neck are thrown back. The vein is then vulnerable to suprasternal incisions (e.g. tracheotomy). The commencement of the vein receives the thoracic duct, which often divides into two or three branches that join the vein separately. In addition to the vertebral and internal thoracic veins the left brachio¬cephalic vein receives most of the blood from the inferior thyroid plexus of veins. The left superior intercostal vein joins it near the midline of the body and a large thymic vein commonly enters nearby.