THE MEDIASTINUM. 



189 



the median line and the edges of the lungs which meet opposite the second rib give 

 a resonant percussion note to the first piece of the sternum. With all these 

 important structures crowded in the small space between the vertebrae and sternum 

 it is easy to see why tumors in this region should cause serious symptoms. 



Aneurism involving the arch of the aorta and the great vessels is common. 

 Tumors, such as sarcoma, carcinoma, and glandular, though rare, do occur. 

 Abscess from high dorsal Pott's disease has been known to cause serious effects. 



The symptoms of all these affections resemble one another to a considerable 

 extent. Interference with the blood-current, usually in the veins, almost never in 

 the arteries, is marked. Alteration in the voice is produced by pressure on the 

 recurrent laryngeal nerves. Dyspnoea from the pressure on the trachea and diffi- 

 culty in swallowing also occur, as well as interference with the circulation and the 



Vagus nerve 

 Internal jugular vein 

 Common carotid artery 

 Subclavian vein 



Left innominate 

 vein 



Phrenic nerve 

 Subclavian artery 

 Vagus nerve 



Descending 

 vena cava 

 Left pulmonary _ 

 artery 



Left bronchus 



Left pulmonary,, 

 veins 



Right atrium 



(auricle) 



Aorta 



Trachea 



Bronchial 



lymph-node 



Pulmonary 



artery 



Pulmonary 



Veins 



Right ventricle 





FIG. 209. Contents of the mediastina viewed from the front. 



action of the heart. The presence of growths in this region is indicated also by the 

 presence of dulness over the region of the manubrium. 



Anterior Mediastinum. This is the space below the second costal cartilages, 

 between the sternum in front, the pericardium behind, and the two pleurae on the 

 sides. It is only a narrow slit in the median line above from the second to the 

 fourth costal cartilage; from here the right pleura is prolonged obliquely down and 

 outward to the seventh costal cartilage, which it follows. On the left side the pleura 

 leaves the median line about the fourth cartilage and passes out about 2 cm. to the 

 left of the sternum and then down to the seventh costal cartilage, which it follows. 

 The triangularis sterni muscle arises from the under surface of the lower third of the 

 sternum and from the xiphoid cartilage and passes upward and outward to insert 

 into the costal cartilages of the second to the sixth ribs inclusive. The -muscle lies 

 in front of the anterior mediastinum and the internal mammary artery runs down 

 between it and the bone about i cm. distant from the edge of the sternum. There 

 are a few lymphatic nodes in the anterior mediastinum on the diaphragm below and 



