40 THORAX 



azygos. The left lung in the corresponding situation is 

 marked by a deep longitudinal groove which is produced 

 by the contact of the lung with the descending thoracic 

 aorta ; and, close to the base, a small triangular area, anterior 

 to the aortic groove, lies in relation with the left border of 

 the lowest part of the thoracic portion of the oesophagus. 



The portion of the mediastinal surface which lies above 

 the hilus and pericardial hollow is applied to the lateral 

 aspect of the superior mediastinum and the markings upon 

 it are different on the two sides. On the left side a broad 

 deep groove, caused by the aortic arch, curves over the hilus 

 and becomes continuous posteriorly with the aortic groove 

 on the posterior mediastinal area. From this arched groove 

 a sharply cut sulcus, caused by the left subclavian artery, 

 ascends on the medial side of the apex and, turning laterally 

 above, it crosses the anterior border of the apex a short 

 distance below the summit. Immediately anterior to the 

 subclavian sulcus the medial surface of the apex is occasion- 

 ally marked by a shallow sulcus caused by the lateral margin 

 of the left innominate vein, and more inferiorly its anterior 

 margin is depressed by the first rib. That portion of the 

 surface which lies posterior to the subclavian sulcus is 

 separated by areolar tissue from the oesophagus. 



On the right lung also a curved sulcus arches over the 

 hilus. It is caused by the vena azygos, as it passes anteriorly 

 to join the superior vena cava. This groove is much narrower 

 and less distinct than the sulcus on the left lung due to the 

 aortic arch. From the anterior end of the sulcus for the 

 azygos vein a broad shallow sulcus passes upwards to the 

 lower and anterior part of the apex. This is produced by 

 the superior vena cava and the innominate vein, and in some 

 cases it is prolonged to the upper part of the apex by a 

 slight longitudinal depression due to the pressure of the 

 internal jugular vein. Arching laterally, across the upper 

 part of the anterior aspect of the apex, there is a shallow groove 

 produced by the right subclavian artery. Posterior to the sulcus 

 for the innominate vein, the medial surface of the apex lies in 

 relation with the right side of the trachea, and still further 

 posteriorly it is either in relation with the right lateral border 

 of the superior mediastinal part of the oesophagus, or it is 

 separated from it by a mass of areolar tissue. 



The anterior and posterior borders of the lung are in 



