THE AORTA. 



209 



compressed between the trachea and vertebrae with the thoracic duct immediately to 

 the left. The left recurrent laryngeal leaves the pneumogastric on the front of the 

 arch, then winds around it and ascends between the trachea and oesophagus to reach 

 the larynx above. Above, from the upper surface of the aorta, are given off the 

 innominate, left carotid, and left subclavian arteries. The left innominate vein crosses 

 above its upper edge to unite with the right innominate to form the superior cava. 

 Below is the left bronchus coming off from the bifurcation of the trachea, and wind- 

 ing around the arch is the left recurrent laryngeal nerve. Beneath the arch and 

 in front of the bronchi are the right and left pulmonary arteries. From the latter the 

 ductus arteriosus goes to the arch. The cardiac branches of the pneumogastric and 

 sympathetic nerves lie on the anterior, inferior, and posterior sides of the arch. 



Vagus nerve. 



Common carotid 



artery 



Internal jugular vein 



Subclavian vein 



Innominate artery 



Right recurrent 



laryngeal nerve 



Right innominate 



vein 



Phrenic nerve 



descending vena 

 cava 



Aorta 



Right auricle 

 (atrium) 



Right coronary 

 artery- 



Vagus nerve 

 Common carotid artery 

 Internal jugular vein 

 ubclavian vein 



Left innominate vein 

 Phrenic nerve 



Left recurrent 

 laryngeal nerve 



Ductus arteriosus 

 Pulmonary artery 



Left bronchus 



Pulmonary veins 



Left coronary artery 

 Left ventricle 



Right ventricle 



FIG. 222. Heart and great blood-vessels. 



The ductus arteriosus at birth is about i cm. long and runs from the pulmo- 

 nary artery to the arch of the aorta below the left subclavian artery. It serves in the 

 foetus to carry the blood from the trunk of the pulmonary artery direct to the aorta 

 instead of passing into the lungs. When, after birth, the lungs are used the ductus 

 arteriosus becomes obliterated and is found later in life as a cord running to the 

 under side of the arch of the aorta. Congenital defects in the heart are a frequent 

 cause of death at birth and in infancy and childhood. They cause an undue mixture 

 of the venous and arterial blood and give the surface a dusky, bluish hue, hence the 

 term " blue baby " as applied to this condition. It is due to an absence of a part 

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