THE THORACIC AORTA. 605 



Surgical Anatomy. Wounds of the palmar arches are of special interest, and are always 

 difficult to deal with. Wheu the wound in the superficial tissues is extensive, it may be possible 

 to secure the bleeding ends of the vessel : but when there is a small punctured wound, as from 

 a penknife or piece of glass, pressure systematically applied is probably the best course of treat- 

 ment, as there is difficult} 7 in reaching the wounded vessel without d'amaging important struc- 

 tures. At the same time it must be admitted that pressure applied to the palm of the hand to 

 arrest hemorrhage from a wound of one of the palmar arches, especially the deep arch, is apt 

 to be followed by sloughing, owing to the rigidity of the parts and the facility with which a con- 

 siderable amount of pressure can be applied. 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 ligature one of the arteries of 

 the forearm alone, and indeed simultaneous ligature of both radial and ulnar arteries above the 

 wrist is often unsuccessful, on account of the anastomosis carried on by the carpal arches. 

 Therefore, upon the failure of pressure to arrest haemorrhage it is expedient to apply a liga- 

 ture to the brachial artery. 



THE DESCENDING AORTA. 



ARTERIES OF THE TRUNK. 



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 THOEACIC AORTA. 



The Thoracic Aorta commences at the lower border of the fourth dorsal ver- 

 tebra, on the left side, and terminates at the aortic opening in the Diaphragm, in 

 fp.nt of the last dorsal vertebra. At its commencement it is situated on the left 

 side of the spine : it approaches the median line as it descends, and at its termina- 

 tion lies directly in front of the column. The direction of this vessel being influ- 

 enced by the spine, upon which it rests, it describes a curve which is concave forward 

 in rhe dorsal region. As the branches given off from it are small, the diminution 

 in the size of the vessel is inconsiderable. It is contained in the back part of the 

 posterior mediastinum. 



Eelations. It is in relation, in front* from above downward, with the left pul- 

 monary artery, the left bronchus, the pericardium, and the oesophagus ; behind. 

 with the vertebral column and the vena azygos minor ; 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 at first on the right side 

 of the aorta, but at the lower part of the thorax it gets 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. 



Left pulmonary artery. 

 Left bronchus. 

 Pericardium. 

 (Esophagus (below). 



Right side. \ Left side. 



(Esophagus Thoracic \ Pleura. 



Vena azygos major. y Aoru. I Left l un g. 



Thoracic duct. V J (Esophagus (below). 



Behind. 



Vertebral column. 

 Vena azygos minor. 



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. \\ hether this is the result of 

 disease or of congenital malformation is immaterial to our present purpose ; it affords an interest- 

 ing opportunity ot observing the resources of the collateral circulation. The course of the anas- 

 tomosing vessels, by which the blood is brought from the upper to the lower part of the artery, 

 will be found well described in an account of two cases in the Pathological Transactions, vols. viii. 

 and x. In the former (p. 160 j Mr. Sydney Jones thus sums up the detailed description of the 



