THE DESCENDING AORTA 655 



encircle the vessel with a ligature, a pair of hemostatic forceps may be applied and left on for 

 twenty-four or forty-eight hours. Wounds of the deep arch are not so easily dealt with. It may 

 be possible to secure the vessel by ligature or by forcipressure forceps, which may be left on; 

 or, failing in this, the wound may be carefully plugged with gauze and an outside dressing care- 

 fully bandaged on. The plug should be allowed to remain untouched for three or four days. 

 In wounds of the deep palmar arch a ligature may be applied to the bleeding points from the 

 dorsum of the hand by resection of the upper part of the third metacarpal bone. It is useless 

 in these cases to ligate one of the arteries of the forearm alone, and, indeed, simultaneous liga- 

 tion of both radial and ulnar arteries above the wrist is often unsuccessful, on account of the 

 anastomosis carried on by the carpal arches. Therefore, if unable to ligate the divided ends 

 of the arch, upon the failure of pressure to arrest hemorrhage, it is expedient to apply a ligature 

 to the brachial artery. 



ARTERIES OF THE TRUNK. 

 THE DESCENDING AORTA (Figs. 466, 467). 



The descending aorta is divided into two portions, the thoracic and abdominal, 

 in correspondence with the two great cavities of the trunk in which it is situated. 



The Thoracic Aorta (aorta thoracalis] (Fig. 466). The thoracic aorta is 

 contained in the back part of the posterior mediastinum and commences at the 

 lower border of the fourth thoracic vertebra, on the left side, and terminates at 

 ~lhe aortic opening in the Diaphragm, in front of the lower border of the last 

 thoracic vertebra. At its commencement it is situated on the left side of the 

 vertebral column; it approaches the median line as it descends, and at its 

 termination lies directly in front of the vertebral column. The direction of this 

 vessel being influenced by the vertebral column, upon which it rests, it describes 

 a curve which is concave forward in the thoracic region. As the branches given 

 off from it are small, the diminution in the size of the vessel is inconsiderable. 



Relations. It is in relation, in front, from above downward, with the root of the left lung, 

 the pericardium, the oesophagus, and the Diaphragm; behind, with the vertebral column and 

 the azygos minor veins; on the right side, with the vena azygos major and thoracic duct; on the 

 left side, with the left pleura and lung. The oesophagus, with its accompanying nerves, lies on 

 the right side of the aorta above; but at the lower part of the thorax it passes in front of the 

 aorta, and close to the Diaphragm is situated to its left side. 



PLAN OF THE RELATIONS OF THE THORACIC AORTA. 



In front. 



Root of left lung. 

 Pericardium. 

 (Esophagus (middle). 

 Diaphragm. 



Right side. /^ ^\ Left side. 



(Esophagus (above). [ Thoracic | Pleura. 



Vena azygos major. I orta- j Left lung. 



Thoracic duct. \ ., / (Esophagus (below). 



Behind. 



Vertebral column. 



Superior and inferior azygos minor veins. 



Peculiarities. The aorta is occasionally found to be obliterated at a particular spot viz., 

 at the junction of the arch with the thoracic aorta just below the ductus arteriosus. Whether 

 this is the result of disease or of congenital malformation is immaterial to our present purpose; 

 it affords an interesting opportunity of observing the resources of the collateral circulation. 



