The veins of the thorax are: the pulmonary, which carry the blood from the lungs to the left side of the heart; and the superior vena cava and its tributaries, which return the venous blood from the head and neck, the upper extremities, and the walls of the thorax, to the right side of the heart. The inferior vena cava, which brings back the blood from the abdomen and pelvis and lower extremities, is described with the veins of the abdomen, in which cavity it lies throughout by far the greater part of its course, somewhat less than half an inch of its upper end only being situated in the thorax.
The pulmonary veins are contained in the middle mediastinum. The superior vena cava and the right and left innominate veins course through the superior mediastinum. The azygous veins, the larger of which opens into the superior vena cava, lie on either side of the thoracic vertebra in the posterior mediastinum. They receive the intercostal, the bronchial, and the esophageal veins.
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.
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