256 HUMAN ANATOMY. 



MEDIASTINUM. 



The mediastinum is the space left between the two pleurae 

 in the median line between the sternum and vertebral column, 

 and contains the heart within its pericardium and all the thoracic 

 viscera except the lungs. The intervals in the mediastinum from 

 their position are named anterior, middle, posterior, and superior 

 mediastinal cavities. The boundaries and contents of the four 

 mediastinal cavities are as follow : 



Anterior mediastinum, bounded in front by the sternum; 

 laterally, pleura ; behind, the pericardium. It contains : 



Triangularis sterni muscle; 



Remains of thymus gland; 



Left internal mammary artery and vense comites ; 



Lymphatic vessels from convex surface of the liver; 



Areolar connective tissue. 



Middle mediastinum, bounded in front by the anterior 

 mediastinum ; laterally, by the pleura ; behind, posterior media- 

 stinum. It contains : 



Ascending portion of aorta; 



Superior vena cava; 



Heart, inclosed in the pericardium; 



Bifurcation of trachea; 



Pulmonary artery and veins; 



Phrenic nerves; 



Arteriae comites nervi phrenici, from the internal mammary. 



Posterior mediastinum, bounded in front by the pericardium 

 and root of the lungs; behind, vertebral column; laterally 

 pleura. It contains: 



(Esophagus; Vena azygos major; 



Thoracic duct; Vena azygos minor; 



Descending aorta; Superior intercostal veins; 



Lymphatic glands and vessels; Pneumogastric nerves; 



Great splanchnic nerves. 



The superior mediastinum is that portion of the mediastinal 

 space above the upper border of the fifth thoracic vertebra. It is 

 bounded in front by the manubrium sterni ; behind, by the upper 

 dorsal vertebra; laterally, by the pleura. It contains: 



Origin of sterno-thyroid muscle; Left superior intercostal vein; 



Origin of sterno-hyoid muscle; Left recurrent laryngeal nerves; 



Lower end of the longus colli muscle; Cardiac nerves; 



Innominate artery; Pneumogastric nerves; 



Left carotid artery; Phrenic nerves; 



Subclavian artery; (Esophagus; 



Transverse portion of the aorta; Trachea; 



Innominate veins; Thoracic duct; 



Superior vena cava; Remains of the thymus gland; 



Lymphatics. 



