THORACIC CAVITY 49 



Posterior to its lower part is the trachea, but as the artery passes 

 upwards and to the right it gains the side of the trachea and 

 has the upper part of the lung and pleura posterior to it. 

 To its left, at its commencement, is the left common carotid 

 artery, and at a higher level the trachea. On its right side 

 is the right innominate vein, which separates it from the right 

 phrenic nerve and the pleura. As a rule it gives off its 

 terminal branches only, but occasionally a small artery, called 

 the thyreoidea ima, springs from it. 



The Thyreoidea Ima. This artery is frequently absent. When it is 

 present it springs from the innominate artery, or from the arch of the aorta, 

 and runs upwards, anterior to the trachea, to the thyreoid gland. 



Arteria Carotis Communis Sinistra. The left common 

 carotid artery springs from the arch of the aorta immediately 

 to the left of, and slightly posterior to, the innominate artery. 

 It passes upwards, through the superior mediastinum and 

 posterior to the left sterno-clavicular joint, into the neck. Its 

 anterior relations in the thorax are similar to those of the 

 innominate artery. Posterior to it, from below upwards, are the 

 trachea, the left recurrent nerve, the oesophagus and the 

 thoracic duct, and, on a plane somewhat more to the left, the 

 left phrenic and vagus nerves, and the subclavian artery. To 

 its right lie first the innominate artery, and then the trachea ; 

 and to its left is the left pleura. It gives off no branches in 

 the thorax. 



Arteria Subclavia Sinistra. The left subclavian artery 

 springs from the posterior part of the aortic arch, posterior to 

 the left common carotid. It passes vertically upwards, through 

 the superior mediastinum and posterior to the sternal end of 

 the clavicle, into the root of the neck. Anterior to it are the 

 left phrenic and vagus nerves, which separate it from the 

 left common carotid artery. Posterior, and to its left side, it 

 is in relation with the left mediastinal pleura and the lung. 

 To its right side are the trachea and the left recurrent 

 nerve, and, at a higher level, the oesophagus and the 

 thoracic duct. It gives off no branches in the thoracic part 

 of its course. 



Dissection. The lateral walls of the pericardium have already been 

 exposed and opened (see p. 33) ; the flaps then made should be replaced 

 and fixed in position. When this has been done, the outline of the sac 

 will be fully displayed, and the dissectors can then study its relations to 

 adjacent organs. 

 VOL. II 4 



