<Tr> <Th> FMA </Th> <Td> 4720 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart . It is a large - diameter (24 mm), yet short, vein that receives venous return from the upper half of the body, above the diaphragm . (Venous return from the lower half, below the diaphragm, flows through the inferior vena cava .) The SVC is located in the anterior right superior mediastinum . It is the typical site of central venous access (CVA) via a central venous catheter or a peripherally inserted central catheter . Mentions of "the cava" without further specification usually refer to the SVC . </P> <P> It is formed by the left and right brachiocephalic veins (also referred to as the innominate veins), which also receive blood from the upper limbs, eyes and neck, behind the lower border of the first right costal cartilage . It passes vertically downwards behind first intercostal space and receives azygos vein just before it pierces the fibrous pericardium opposite right second costal cartilage and its lower part is intrapericardial . And then, it ends in the upper and posterior part of the sinus venarum of the right atrium, at the upper right front portion of the heart . It is also known as the cranial vena cava in other animals . </P>

Where does the blood in the superior vena cava come from