180 Arch of Aorta 



Irregularities of the aortic arch. Sometimes the heart and 

 aorta, and the arterial and venous trunks associated with them, are 

 transposed, so that the apex beats on the right of the sternum, the 

 superior cava being on the left of the middle line, and the aorta arching 

 to the right. But the aorta may, by the development of the right fourth 

 branchial arch instead of the left, bend over to the right side, without 

 there being any other transposition of thoracic viscera. 



The right subclavian artery may come from the back of the left end 

 of the arch, and reach the left scaleni by passing behind the trachea 

 and oesophagus. 



There may be two innominate arteries ; the left carotid may come 

 from the (right side) innominate ; the two carotids may come off to- 

 gether, the subclavians arising on either side of the common trunk; the 

 left vertebral may come off as a fourth trunk between the left carotid 

 and subclavian ; both vertebrals may thus arise, making five trunks. 

 All four large trunks may arise separately, there being no innominate 

 artery. Further, the vertebrals may arise separately, whilst the innomi- 

 nate may be divided, making six. The left carotid coming from the 

 innominate may cross the windpipe dangerously near the knife of the 

 tracheotomist (p. 133). 



On account of the enormous strain which is thrown on the beginning 

 of the aorta its wall is apt to yield, especially when weakened by disease 

 arteritis. Aneurysm is thus produced. The very root of the aorta 

 being dilated, the valves fail to prevent regurgitation, and a diastolic 

 murmur occurs. The first part of the arch is more likely to yield than 

 the second, for the former is enclosed within the pericardium, whilst 

 the latter has its walls strengthened by the fibrous part of the pericar- 

 dium being blended with it. A fatal leakage of an aneurysm of the first 

 part may take place into or through the pericardium, but before this 

 happens certain pressure effects may be noticed; these, however, are not 

 so varied and suggestive as they are in aneurysm of the transverse arch, 

 for the tumour bulges forwards and usually bursts before it gets large. 

 When it reaches the chest-wall a pulsating swelling occurs near the 

 second or third right cartilage. 



Tight-lacing, or tight clothing, especially about the neck and upper 

 part of chest, is apt to check the emptying of the large vessels and to 

 produce thoracic aneurysm. 



The general effects of thoracic aneurysm are disturbance of the 

 action of the heart by the pressure upon cardiac and pneumogas- 

 tric filaments. Through the pneumogastric interference ' indigestion ' 

 may be complained of. The growth of the tumour displaces the lung 

 and makes percussion dull. Later, there may be pain in the chest and 

 back, especially when the swelling impinges against the spine. Pres- 

 sure upon the root of the lung may cause dyspncea, with strange breath 

 sounds and cough. The patient may be unable to lie down in comfort, 

 as the tumour then weighs the more heavily against the trachea. The 



