190 



APPLIED ANATOMY. 



in the superior mediastinum on the arch of the aorta and left innominate vein above. 

 A chain of nodes also accompanies the internal mammary artery along the edge of 

 the sternum between the pleura and chest wall. 



Abscess of the anterior mediastinum may result from infection due to injury or 

 punctured wounds. It may break into the pleurae on the sides, into the pericar- 

 dium posteriorly, work its way down toward the abdomen, or point in the intercostal 

 spaces at the edge of the sternum. 



Paracentesis pericardii is performed in the sixth interspace close to the sternum; 

 also, the fifth and sixth cartilages may be resected, the internal mammary artery 

 ligated, and the pericardium opened and even drained. 



If one attempts to pass a trochar into the pericardium by a puncture through 

 the fifth or sixth interspace sufficiently far out to avoid wounding the internal 

 mammary artery the pleura is apt to be wounded, as it passes farther toward the 

 median line than does the lung. 



The Middle Mediastinum. The middle mediastinum is limited in front by 

 the anterior wall of the pericardium and behind by the posterior wall of the pericar- 

 dium and roots of the lungs. It contains the heart with the lower half of the descend- 

 ing vena cava and the vena azygos major emptying into it, and the ascending aorta ; 



Esophagus 

 Vagus nerve 

 Phrenic nerve 



Vena azygos major 

 Right bronchus 



Right pulmonary artery 

 Pulmonary vein 



Thoracic duct 

 Phrenic nerve 

 Recurrent laryngeal nerve- 

 Common carotid artery 



Bronchial artery. 



Pulmonary artery 

 Left vagus nervi 



Left bronchu 



Pulmonary vein 

 Aort 



Thoracic duct 

 Vena azygos major - 



FIG. 210. Contents of the mediastina viewed from the rear. 



also the structures forming the roots of the lungs, viz. , the right and left bronchi, 

 and the pulmonary arteries and veins* The phrenic nerves lie between the pericar- 

 dium and pleurae anteriorly. 



The bronchial lymphatic nodes are numerous between the structures forming the 

 roots of the lungs. It is these nodes that are so often enlarged in diseases of the 

 lungs. They are affected in malignant disease as well as in tuberculosis, etc. Enlarge- 

 ments of the heart pressing on the vessels, particularly the vena azygos major, are 

 sometimes thought to cause pleural effusions, especially if one-sided. 



When the pericardium is distended with fluid it enlarges more in an up and down 

 direction, but when the heart is enlarged its size increases mainly laterally from side 

 to side. 



Posterior Mediastinum. The posterior mediastinum extends from the peri- 

 cardium and roots of the lungs anteriorly to the vertebrae posteriorly. The pleurae 

 are on each side. Behind the pericardium runs the cesophagus, lying in front of the 

 aorta, which rests on the vertebrae. In the chink between the aorta and bodies of 

 the vertebrae lies the thoracic duct and immediately to its right side is the vena azygos 



* The mediastina are arbitrary divisions, and it is a question as to whether the roots of the 

 lungs should not be included in the posterior instead of the middle mediastinum. 



