THORACIC CAVITY 



69 



of the aorta have been cleaned, clean the arch itself. Then 

 carefully remove the areolar tissue which lies between the 

 innominate and left common carotid arteries and display the 

 anterior surface of the trachea. Occasionally a small artery, 

 the thyreoidca ima, will be found ascending on the front of the 

 trachea. It springs either from the arch of the aorta or from 

 the innominate artery. Lastly, clean the areolar tissue from 

 the anterior surface of the pericardium, and then proceed to the 

 study of the structures exposed. 



Left innomi- 

 nate vein 

 Innominate 

 artery 



Phrenic nerve 



Left common 



carotid artery 



Vagus nerve 



Left subclavian 



artery 



'Recurrent nerve 



Mediastinal 

 pleura 

 Thoracic du 



Cartilage of 

 ""first rib 

 Internal mam- 

 mary vessels 

 Right innomi- 

 nate vein 

 Phrenic nerve 



.Trachea 



.Vagus 



(Esophagus 



Mediastinal 

 pleura 



FIG. 29. Transverse section through the Superior Mediastinum 

 at level of the third thoracic vertebra. 



Arteria Anonyma. The innominate artery is the largest 

 of the three great branches of the aortic arch. It com- 

 mences, from the upper border of the arch, posterior and 

 somewhat to the left of the centre of the manubrium sterni 

 (Fig. 30), passes upwards and to the right, and terminates, 

 posterior to the upper border of the right sterno-clavicular 

 articulation, by dividing into the right common carotid 

 and the right subclavian arteries (Fig. 27). Anterior to 

 it are the manubrium sterni, with the attachments of the 

 sterno-hyoid and thyreoid muscles, the right sterno-clavicular 

 joint, the remains of the thymus, and the left innominate vein. 



