272 CLINICAL APPLIED ANATOMY. 



even to a thyroidea ima artery, or a right subclavian with an 

 abnormal origin to the left of the mid-line. In childhood the 

 aorta may reach to the upper border of the manubrium, but at 

 this period of life aneurysm is usually out of question. The 

 ductus arteriosus, which connects the origin of left branch of 

 the pulmonary artery with the aorta joins the latter just beyond 

 the point of origin of the left subclavian artery. The cicatrix 

 can easily be recognised when the aorta is laid open, and is often 

 the site of atheroma. At this part of the aorta is a normal con- 

 striction known as the aortic isthmus, whilst beyond it the vessel 

 often shows a fusiform dilatation which is not aneurysmal, and 

 is called the aortic spindle. The arch of the aorta is moulded 

 on the left aspect of the lower end of the trachea. It leaves its 

 impress on this tube, and forces it decidedly to the right of the 

 mid-line. An aneurysm of the arch may increase the tracheal 

 displacement, so that even in the neck the air tube may be 

 found to be shifted towards the right side. On the left aspect of 

 the arch also lie the oesophagus, the left recurrent laryngeal nerve, 

 and the thoracic duct. All of these structures may be subjected 

 to pressure. An aneurysm in this region may open into the 

 oesophagus. When the trachea is compressed stridor may be 

 heard over both lungs, and is associated with a brassy cough 

 and paroxysmal dyspnoea. The cough and dyspnoea are probably 

 caused by irritation of the filaments which the vagi supply to 

 the trachea. 



The right lung and pleural sac are fairly well protected by the 

 intervention of the structures already mentioned as being in 

 immediate relation with the right side of the aortic arch, but 

 aneurysms near the commencement of the arch may invade the 

 right pleural sac. 



The left side of the arch is in relation from before backwards 

 with the left phrenic nerve, the superficial cardiac branches of 

 the left vagus and left sympathetic, the left vagus nerve and the 

 left superior intercostal vein. These are the only structures 

 which intervene between the aortic arch and the left lung and its 

 pleural envelope. A deep impression is made by the artery on 



