THE MEDIASTINUM. 



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which contains the pericardium and its contents, the middle mediastinum ; that 

 part which is in front of the pericardium, the anterior mediastinum ; and that 

 part which is behind the pericardium, the posterior mediastinum. 



FIG. 708. The posterior mediastinum. 



The superior mediastinum is that portion of the interpleural space which lies 

 above the upper level of the pericardium, between the manubrium sterni in front and 

 the upper dorsal vertebrae behind. It is bounded below by a plane passing back- 

 ward from the junction of the manubrium and gladiolus sterni to the lower part 

 of the body of the fourth dorsal vertebra. It contains the origins of the Sterno- 

 hyoid and Sterno-thyroid muscles and the lower ends of the Longi colli muscles ; 

 the transverse portion of the arch of the aorta ; the innominate, the thoracic 

 portion of the left carotid and subclavian arteries ; the upper half of the superior 



