THORACIC CAVITY 97 



and the vena azygos, which enters it immediately before 

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

 right costal cartilage (Fig. 15). 



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, trachea and the vena azygos on the left 

 (Figs. 23, 57), and, at a lower level, the right bronchus, the 

 right pulmonary artery (Fig. 20) and the upper right 

 pulmonary vein pass behind it. 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 ascend- 

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

 phrenic nerve and the accompanying vessels intervening 

 (Figs. 20, 56). 



Vena Cava Inferior. Only a small portion, about 18 mm. 

 (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 liga- 

 mentum pulmonis, and immediately ends in the lower and 

 posterior angle of the right atrium (Figs. 13, 15, 59). 



Relations. Anterior to it is the diaphragm ; posterior to it 

 the vena azygos, the greater splanchnic nerve and the thoracic 

 duct \ and to its right the phrenic nerve with its accompanying 

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



Dissection. 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 end of the anterior longitudinal 

 sulcus and terminate a little to the left of the coronary sulcus. 

 The second must commence at the right end of the first and pass 

 obliquely downwards and to the right, along the left margin of 

 the coronary sulcus, to the inferior border of the heart. The 

 third commences at the left end of the first, follows the line of 

 the anterior interventricular sulcus, lying a little to its right 

 side, and also terminates at the lower margin of the heart. 

 After the triangular flap thus formed is turned downwards and 

 to the right, the cavity of the ventricle should be cleaned with the 

 aid of sponge and forceps. If the moderator band of muscle 

 fibres, which connects the anterior wall of the ventricle with the 

 interventricular septum, interferes with the necessary displace- 

 ment of the flap it must be divided. 

 VOL. II 7 



