THOEACIC ANEURYSMS. 271 



portions of the aorta sometimes rupture into the right pleural 

 sac, which lies close by. 



The outline of a healthy ascending aorta normally presents 

 several bulgings. The great sinus of the aorta, which is a 

 longitudinal projection of its right border, must not be mistaken 

 for an aneurysmal dilatation ; it is occasionally present in the 

 foetus, but is best marked in old age. The three sinuses of 

 Valsalva project near the root of the vessel. They correspond 

 to the positions of the aortic valves. Aneurysm of the right 

 sinus has opened directly into the right ventricle, with which the 

 sinus is in relation ; aneurysm of the anterior sinus has been 

 known to open into the left ventricle. But such aneurysms are 

 more likely to open into the pericardium with fatal results. 

 These sinus aneurysms may compress and actually obliterate 

 the adjacent branches of the coronary arteries. The orifices of 

 the coronary arteries lie in the anterior and left posterior sinuses, 

 and may be narrowed by the endarteritis which is associated 

 with aneurysm, causing anginal symptoms. Aneurysmal dilata- 

 tion of the ascending aorta has a tendency to displace the heart 

 downwards, and disease of this part of the vessel is often 

 associated with incompetence of the aortic valves which lie at 

 its orifice. 



The arch of the aorta is the oblique segment, often loosely 

 termed transverse, which lies in the superior mediastinum. It 

 passes from behind the right side of the sternum at the level of 

 the second costal cartilage, at first upwards, backwards, and to 

 the left, and then directly backwards to the left side of the fourth 

 dorsal vertebra, at the lower border of which it becomes the 

 descending aorta. 



An aneurysm in this situation may impair the percussion 

 note of the sternum or give rise to pulsation at the root of the 

 neck. The upper border of the arch as it crosses the mid-line 

 is usually an inch below the interclavicular notch of the sternum, 

 so its pulsation cannot be readily felt, moreover, even when 

 pulsation is recognised in this situation it may be due to the 

 innominate or left common carotid arteries near their origins, or 



