ArcJi 'of Aorta 



right auricular appendix. Behind is the root of the right lung. To 

 the right are the superior vena cava and the right auricle, and to the 

 left is the pulmonary artery (v. p. 185). 



The second part inclines backwards, and to the left, from the second 

 right cartilage, gently bending over the trachea, till it reaches the left 

 side of the fourth dorsal vertebra. 



Relations. /// front are the left pleura and lung, and the left 

 pneumogastric, phrenic, and cardiac nerves. The left innominate vein 

 may overlap it above, and the left superior intercostal vein ascends 

 obliquely in front to join the left innominate. Behind are the trachea, 

 oesophagus, thoracic duct ; the left recurrent laryngeal, and the deep 

 cardiac nerves. Above are given off the innominate, the left carotid, 

 and the left subclavian arteries ; the left innominate vein runs across 

 the roots of those arteries. Below are the bifurcation of the pulmonary 

 artery, the ductus arteriosus, and the left recurrent laryngeal nerve. 



This part of the arch is badly named ' transverse,' as it runs almost 

 directly backwards from the second right cartilage. 



Its upper border is about an inch below the episternal notch, and 

 corresponds with the tip of the third dorsal spine, and its lower border 

 is on the level of the transverse sternal ridge. But in feeble and small- 

 chested persons the transverse aorta may lie on the level of the top of 

 the manubrium ; in big-chested men it is placed much deeper behind 

 the top of the gladiolus, for instance. Its concavity is, of course, 

 downwards, but there is a second concavity directed backwards and to 

 the right which is due to the vessel being bent round the trachea. 



The third part of the arch is very short, extending only down the 

 left side of the fifth dorsal vertebra, which thus forms its posterior 

 relation. In front is the root of the left lung, and on the right side are 

 the fifth vertebra, and the oesophagus and thoracic duct ; on the left 

 are the lung and pleura. 



To mark out the large vessels. The aorta begins opposite the 

 sternal end of the third left space. Roughly, it is about as wide as the 

 thumb. It slopes upwards to the second right cartilage. Thence it 

 turns backwards, and slightly to the left, behind the manubrium, its 

 lower border corresponding with the ridge between the manubrium and 

 the gladiolus. The third part descends by the fifth dorsal vertebra, 

 rather to the left of the middle line. 



From immediately behind the middle of the manubrium the inno- 

 minate artery and the left common carotid mount to their respective 

 sterno-clavicular joints. The left subclavian ascends a little to the 

 outer side of the left carotid. 



The pulmonary artery, two inches long, ascends in the pericardium 

 from the right ventricle to the concavity of the aortic arch, where it bi- 

 furcates ; that is, it reaches from the third left chondro-sternal joint 

 (the situation of the pulmonary valve) to the second left chondro-sternal 

 joint. 



