30 THORAX 



at the level of the second costal cartilage (see Fig. 12). As 

 it turns anteriorly the vein lies immediately to the right side 

 of the oesophagus, trachea and vagus nerve. 



The tributaries of the vena azygos are : (i) The right 

 superior intercostal vein which drains blood from the 

 greater part of the second and third intercostal spaces. 

 (2) The eight lower intercostal veins and the subcostal vein 

 of the right side. (3) The vena hemiazygos, and frequently 

 (4) the vena hemiazygos accessoria. Both the latter enter it 

 from the left. In many cases the accessory azygos vein joins 

 the hemiazygos vein. (5) Two or more bronchial veins from 

 the right lung. (6) Some veins from the oesophagus. (7) 

 Some minute pericardial veins. 



The vena azygos commences in the abdomen where it 

 anastomoses either with one of the upper lumbar veins or 

 directly with the inferior vena cava. Thus it forms a more 

 or less direct anastomosis between the two venae cavae. 



The intercostal veins and the accompanying arteries and 

 nerves, on both sides, and the hemiazygos and accessory 

 azygos veins will be studied at a later period of the dissection 

 (see p. 108). 



Contents of the Mediastinum and the Structures of the 

 Posterior Part of the Left Half of the Thorax seen from the 

 Left Side. After the removal of the four pleural flaps described 

 on p. 25 the following structures are visible on the left side 

 of the thorax (see Fig. 13). Below and anterior to the root 

 of the lung is the pericardium, covering the left ventricle, the 

 left atrium, the conus arteriosus of the right ventricle and the 

 pulmonary artery. Above the root of the lung is the arch of 

 the aorta. The arch of the aorta terminates posteriorly in 

 the descending aorta, which passes downwards posterior to 

 the root of the lung and the pericardium, but it is separated 

 from the lower part of the posterior wall of the pericardium 

 by the oesophagus, which, at this level, is passing towards 

 the left side. On the left and anterior aspect of the aortic 

 arch, from behind forwards, lie the left vagus nerve, the 

 superior cervical cardiac branch of the left sympathetic 

 trunk, the inferior cervical cardiac branch of the left vagus, 

 and the left phrenic nerve with its accompanying vessels. 

 Crossing the arch obliquely, from behind forwards and 

 upwards, is the left superior intercostal vein, which passes 

 lateral to the vagus and medial to the phrenic nerve. Above 



