322 A MANUAL OF ANA TOMY. 



pand and fill up the chest, their anterior borders will come 

 into contact. The heart will be seen to be contained in a 

 similar membranous sac, the pericardium, though it is much 

 stronger than the pleurae. 



The space between the lungs (and pleurae), sternum, and 

 spine, and reaching from the root of the neck to the 

 diaphragm, is the mediastinum. 



The Mediastinum. Figs. 68 to 72. 



The mediastinal space is the central portion of the 

 thoracic cavity between the pleural sacs laterally, the ster- 

 num and cartilages in front, the vertebral column behind, 

 the diaphragm below, and the superior aperture of the 

 thorax above. 



The mediastinum is divided into several portions, as the 

 superior, anterior, middle, and posterior. 



The superior mediastinum lies behind the first piece of 

 the sternum. In front are the sternal origins of the sterno- 

 hyoid and sternothyroid muscles ; behind, are the four 

 upper dorsal vertebrae and the longus colli muscle. It 

 contains the trachea, oesophagus, and thoracic duct ; trans- 

 verse aorta, innominate artery, the thoracic portions of the 

 left carotid (common), and subclavian arteries ; the innomi- 

 nate veins, the upper portion of the superior vena cava ; the 

 pneumogastric, left recurrent laryngeal, the phrenic, sym- 

 pathetic, and cardiac nerves ; lymphatic and thymus glands ; 

 longus colli, sternohyoid, and sternothyroid muscles. 



The anterior mediastinum is all that portion of the 

 mediastinum anterior to the pericardium. It corresponds 

 to the area of heart dullness. It contains a little areolar 

 tissue and a few small lymphatic glands. 



The middle mediastinum is the central portion of the 

 space. It contains the heart, ascending aorta, pulmonary 



