The superior or descending vena cava carries to the heart the blood returned from the head and neck and upper extremities through the right and left innominate veins, and from the walls of the thorax, either directly through the greater azygos vein, or indirectly through the innominate veins.
It is formed by the confluence of the right and left innominate veins at the lower border of the first right costal cartilage close to the sternum, and, descending from this spot in a gentle curve with its convexity to the right and in a direction slightly backwards and outwards behind the sternal end of the first and second intercostal spaces and second costal cartilage, terminates in the right auricle of the heart on a level with the third right costal cartilage in front and the seventh thoracic vertebra behind. It measures about three inches in length (7-8 cm.). A little more than its lower half (4 cm.) is contained within the pericardium, the serous layer of that membrane being reflected obliquely over it immediately below the spot where it is joined by the vena azygos major, and on a lower level than the reflexion of the pericardium on the aorta. The vena cava superior contains no valve.
In front, in addition to the first and second intercostal spaces and the second costal cartilage, it is covered by the remains of the thymus gland, the interthoracic fascia, and the pericardium, and is overlapped by the right pleura and lung.
Behind are the vena azygos major, the right bronchus, the right pulmonary artery, and the superior right pulmonary vein; and below, the fibrous layer of the pericardium. The serous layer is reflected over the front and sides of the vessel, but not over its posterior part.
To the right side are the right lung and pleura, and the phrenic nerve.
To the left side are the right innominate artery and the first or ascending portion of the arch of the aorta.
In addition to the right and left innominate veins and the vena azygos major, it receives small veins from the mediastinum and pericardium.
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