70 THORAX 



upper extremities, the wall of the thorax, and the upper parts 

 of the walls of the abdomen. It commences, by the union 

 of the right and left innominate veins, at the level of the 

 lower border of the sternal end of the right first costal 

 cartilage ; and it terminates, in the upper and posterior part of 

 the right atrium, at the level of the right third costal cartilage, 

 about half an inch from the right border of the sternum. 

 It lies partly in the superior and partly in the middle 

 mediastinum, and its lower half is within the fibrous pericardium 

 and is partly ensheathed by the serous pericardium. 



Tributaries. The tributaries of the superior vena cava are 

 the two innominate veins, by whose junction it is formed, 

 and the vena azygos, which enters it immediately before 

 it pierces the fibrous pericardium, at the level of the second 

 right costal cartilage. 



Relations. The superior vena cava lies to the right of, 

 and somewhat posterior to, the ascending aorta. Posterior to 

 its upper part are the right pleura and lung on the right, 

 and the right vagus and the vena azygos on the left, and, at 

 a lower level, the right bronchus, the right pulmonary artery, 

 and the upper right pulmonary vein. Anteriorly and on the 

 left it is overlapped by the ascending aorta, and on the right 

 by the right pleura and lung. On its left side above is the 

 lower end of the innominate artery, and below is the ascending 

 aorta ; and on the right side is the right pleura, with the right 

 phrenic nerve and the accompanying vessels intervening. 



The Thoracic Part of the Inferior Vena Cava. Only a 

 small portion, about three-quarters of an inch, of the inferior 

 vena cava is found in the thorax. It ascends from the 

 diaphragm along the mediastinal surface of the right pleura 

 and lung, pierces the pericardium anterior to the lower 

 border of the right ligamentum pulmonis, and immediately 

 ends in the lower and posterior angle of the right atrium. 



Relations. Anterior to it is the diaphragm posterior to it 

 the vena azygos, the splanchnic nerves and the thoracic duct ; 

 and to its right the phrenic nerve with its accompanying 

 vessels and the right pleura and lung (see Fig. 12). 



Ventriculus Dexter. The cavity of the right ventricle 

 should be opened by three incisions. The first should be 

 made transversely across the upper end of the conus arteriosus, 

 immediately below the commencement of the pulmonary 

 artery. It should begin a little to the right of the upper 



