THORACIC CAVITY 71 



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, in a plane somewhat more to the left, the 

 left phrenic and vagus nerves, and the left 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 (Figs. 22, 29). 



Dissection. The lateral walls of the pericardium have 

 already been exposed and opened (see p. 44) ; the flaps then 

 made should be replaced and fixed in position with sutures. 

 When that has been done, the outline of the sac will be fully 

 displayed, and the dissectors can then study its relations to 

 adjacent organs. 



The Pericardium. The pericardium is a fibre-serous sac 

 which lies in the middle mediastinum. It surrounds the heart 

 and the roots of the great vessels which enter and leave the 

 heart. 



The Fibrous Pericardium. The fibrous or outer part of 

 the pericardium is conical in form. Its base rests upon the 

 diaphragm, principally upon the central tendon but also 

 upon the muscular portion, particularly upon the left side. 

 Near the median plane it is blended with the central tendon, 

 and can be separated from it only by the aid of the edge 

 of the scalpel ; more laterally the areolar tissue which 



