THE THORAX 1025 



tenor mediastinal pleura; and the -upper and lower left azygos 

 veins. Inferiorlj^ the oesophagus inclines slightly to the left of the 

 vessel. It is to be noted that the oesophagus has a threefold rela- 

 tion to the descending aorta. At first it lies upon the right side of 

 the vessel ; then directly in front of it ; and finally it inclines 

 slightly to its left side. 



Branches. — ^These are as follows : bronchial, pericardial, oeso- 

 phageal, posterior mediastinal, intercostal, and subcostal. 



The bronchial arteries supply the lungs and the bronchial lym- 

 phatic glands. They are usually three in number — one right and 

 two left. The right bronchial artery arises from the aorta in 

 common with the upper left bronchial artery, or sometimes from 

 the first right aortic intercostal artery. The two left bronchial 

 arteries, upper and lower, arise directly from the aorta, near each 

 other. The arteries enter the respective lungs behind the bronchi, 

 and in their further course and distribution they follow the ramifica- 

 tions of the bronchial tubes. 



The bronchial veins accompany the corresponding arteries. The 

 right vein opens into the right azygos vein ; and the left vein opens 

 either into the upper left azygos vein, or into the left superior inter- 

 costal vein. 



The pericardial branches supply the posterior part of the peri- 

 cardium. 



The (esophageal branches are numerous, and arise at irregular 

 intervals. Superiorly they spring from the right side of the aorta, 

 and inferiorly from its anterior wall. They anastomose freely with 

 one another along the wall of the oesophagus ; superiorly with the 

 oesophageal branches of the inferior thyroid arteries ; and inferiorly 

 with the oesophageal branches of the gastric artery from the coeliac 

 axis, the latter branches entering the thorax through the oesophageal 

 opening of the diaphragm. 



The posterior mediastinal branches are very minute, and supply 

 the lymphatic glands and areolar tissue in the posterior mediastinum. 



The intercostal arteries are arranged in pairs, and are nine in 

 number on each side. They are destined for the lower nine inter- 

 costal spaces, the first two spaces being supplied by the superior 

 intercostal artery, which is a branch of the second part of the sub- 

 clavian on the right side, and of the first part on the left side. 

 They arise in pairs from the posterior wall of the descending aorta, 

 and they pass outwards upon the bodies of the vertebrae to the 

 posterior extremities of the intercostal spaces. The arteries of the 

 right side pass behind the oesophagus, the thoracic duct, and the 

 right azygos vein ; and those of the left side pass behind the upper 

 and lower left azygos veins, according to their level. The arteries of 

 both sides pass behind the gangliated cord of the s\Tnpathetic. 

 The upper right intercostal arteries are longer than those of the 

 left side, on account of the position of the descending aorta on the 

 left side of the vertebral column. All the arteries lie behind the 



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