900 



THE THORAX 



lively in front of and behind it, and a middle mediastinum which contains the 

 heart itself. 



The superior mediastinum has the following boundarii's: — the nianulirium 

 with the origins of tlie stcrno-liyoid and sterno-thyroid muscles in front ; the l)odies 

 of the four highest thoracic V('rtel)r;e behind, with the lower i)ortions of the longus 

 colli muscles; and on each side the })leural sacs. Above, the l)oundary corresponds 

 with the superior aperture of the thorax, and below with a nearly horizontal plane 

 passing backwards from the articulation between the manul»rium and gladiolus of 

 the sternum, to the lower part of the body of the fourth thoracic vertebra. This 



Fig. 522. — Superior View of a Section of the Thorax, passing through the Sternum 

 immediately below the first costo-sternal articulation, through the trachea 

 at its division, and through the body of the fourth thoracic vertebra. 

 (Braune.) 



Arch of aorta 

 PHBENIC NER VE 



SECOND COSTAL CARTILAGE 



Axilla? 1/ if»! 



POSTERIOR SURFACE OF STERNUM 

 I'ena cara superior 



PHRENIC NER VE 



SECOND COSTAL CARTILAGE 



Axillary rein 



THIRD RIB 



SCAPULA 



SCAPULA 

 THIRD RIB 

 FOURTH RIB 



VAGVS NERVE 



BODY OF FOURTH THORACIC VERTEBRA 



iower plane nearly corresponds with the upper part of the pericardium and roots of 

 the lungs. 



The superior mediastinum contains the thoracic portion of the trachea, 

 oesophagus, thoracic duct, the arch of the aorta, the innominate artery, thyroidea 

 ima, and thoracic portions of the left carotid and left subclavian; the innominate 

 veins and upper i)art of the superior vena cava, the terminations of the inferior 

 thyroid and internal mammary veins of both sides, and the superior intercostal vein 

 of the left side; the two pneumogastric nerves, with the left recurrent, the phrenic 

 and cardiac nerves; the thymus gland or its remains, and some bronchial lymphatic 

 glands, with the superior sterno-pericardiac ligaments. 



