THE PULMONARY 



463 



In the f(»tus, the puhiionarv artery (fig. 818) continues its course ui)\var(ls, 

 hackwards, and to the left, under the name of the ductus arteriosus, or ductus 

 Botalli, and opens into the descending aorta just l)elo\v tht- origin of the k-ft 

 suhclavian artery. After birth, that i)ortion of the puhiionary artery whicli 

 extends to the aorta becomes obliterated, and remains merely as a fibrous cord. 



The trunk of the artery with the ductus Botalli was originally the left fifth 

 aortic arch, and the recurrent laryngeal nerve in early foetal life passed below it 

 direct to the larynx. As in the process of develo])ment the heart descends into the 

 tliorax, and the fifth arch assumes a more vertical direction, it comes to pass that 

 the nerve winds round the transverse portion of the aorta, the fourth aortic arch. 



Fig. '317. — .\xterior View of the Heart with the Large Arteries axd Veins. 



(By pennissiou. Royal College of Surgeons Mn.seuni.) 



X^// commnn 



carotid artery Internal jugular vein 

 Right superior thyroid vein Left superior 

 Right common carotid artery i thyroid vein 



Internal jugular vein | | THYROID 



Booy 

 Vertebral lein 



Left vertebral vein 



Sitbclavian x-ein 

 Inferior thyroid veins 



Vena azygos major 



Vena cava superioi 



Aorta 



Right pulmonary artery 



PERICARDIUM 

 RIGHT AURICLE L 



RIGHT VENTRICLE 

 Vena cava inferior 



External jugular vein 



Left subclavian vein 

 Left innominate vein 



Left superior intercostal vein 



DUCTUS ARTERIOSUS 



Left pulmonary artery and 



vein 

 LEFT AURICULAR APPENDIX 



Pulmonary artery 



LEFT VENTRICLE 



and consequently external to the ductus arteriosus (fig. 321). In adult life the cord 

 tormed by the obliterated ductus arteriosus arises a little to the left of the Vjifurca- 

 tion of the pulmonary artery, and receives a slight reflexion from the pericardium 

 as it pierces that membrane. It occasionally remains }iartially unobliterated. 



Relations. — In front, the trunk of the pulmonary artery is covered by the 

 second bone of the sternum, the remains of the thymus gland, and the jiericardium 

 (fig. 319), and at its commencement lies immediately l^ehind the anterior extremity 

 of the second intercostal space, the left lung and ])leura intervening. 



Behind, it lies successively upon the ascending {)art of the arch of the aorta 

 and the left auricle. 



