ARCH OF AORTA. 365 



against this part. The direction of the aneurism is also chiefly towards the right of the median 

 line. If it attains a large size and projects forwards, it may absorb the sternum and the carti- 

 lages of the ribs, usually on the right side, and appear as a pulsating tumor on the front of the 

 chest, just below the manubrium ; or it may burst into the pericardium, or may compress or even 

 open into the right lung, the trachea, bronchi, or oasophagus. 



Regarding the transverse part of the arch, the student is reminded that the vessel lies on the 

 trachea, the oesophagus, and thoracic duct ; that the recurrent laryngeal nerve winds around it ; 

 and that from its upper part are given off three large trunks, which supply the head, neck, and 

 upper extremities. Now an aneurismal tumor taking origin from the posterior part or right 

 aspect of the vessel, its most usual site, may press upon the trachea, impede the breathing, or 

 produce cough, haemoptysis, or stridulous breathing, or it may ultimately burst into that tube, 

 producing fatal hemorrhage. Again, its pressure on the laryngeal nerves may give rise to symp- 

 toms which so accurately resemble those of laryngitis, that the operation of tracheotomy has in 

 some cases been resorted to from the supposition that disease existed in the larynx ; or it may 

 press upon the thoracic duct, and destroy life by inanition ; or it may involve the oasophagus, 

 producing dysphagia; or may burst into this tube, when fatal hemorrhage will occur. Again, the 

 innominate artery, or the left carotid, or subclavian, may be so obstructed by clots, as to produce 

 a weakness, or even a disappearance, of the pulse in one or the other wrist ; or the tumor may 

 present itself at or above the manubrium, generally either in the median line, or to the right of 

 the sternum. 



Aneurism affecting the descending part of the arch is usually directed backwards and to the 

 left side, causing absorption of the vertebrae and corresponding ribs ; or it may press upon the 

 trachea, left bronchus, oesophagus, and the right and left lungs, generally the latter. When rup- 

 ture of the sac occurs, this usually takes place into the left pleural cavity ; less frequently into 

 the left bronchus, the right pleura, or into the substance of the lungs or trachea. In this form 

 of aneurism, pain is almost a constant and characteristic symptom, existing either in the back or 

 chest, and usually radiating from the spine around the left side. This symptom depends upon 

 the aneurismal sac compressing the intercostal nerves against the bone. 



BRANCHES OF THE ARCH OF THE AORTA (figs. 205 and 206). 



The branches given off from the arch of the aorta are five in number. Two 

 of small size from the ascending portion, the right and left coronary ; and three of 

 large size from the transverse portion, the innominate artery, the left carotid, and 

 the left subclavian. 



Peculiarities. Position of the Branches. The branches, instead of arising from the highest 

 part of the arch (their usual position), may be moved more to the right, arising from the com- 

 mencement of the transverse or upper part of the ascending portion ; or the distance from one 

 another at their origin may be increased or diminished, the most frequent change in this respect 

 being the approximation of the left carotid towards the innominate artery. 



The Number of the primary branches may be reduced to two : the left carotid arising from the 

 innominate artery, or (more rarely) the carotid and subclavian arteries of the left side arising 

 from a left innominate artery. But the number may be increased to four, from the right carotid 

 and subclavian arteries arising directly from the aorta, the innominate being absent. In most 

 of these latter cases, the right subclavian arose from the left end of the arch ; in other cases, it 

 was the second or third branch given off instead of the first. Lastly, the number of trunks 

 from the arch may be increased to five or six ; in these instances, the external and internal caro- 

 tids arose separately from the arch, the common carotid being absent on one or both sides. 



Usual Number, but Arrangement different. When the aorta arches over to the right side, the 

 three branches have an arrangement the reverse of what is usual, the innominate supplying the 

 left side ; and the carotid and subclavian (which arise separately) the right side. In other cases, 

 where the aorta takes its usual course, the two carotids may be joined in a common trunk, and 

 the subclavians arise separately from the arch, the right subclavian generally arising from the left 

 end of the arch. 



Secondary Branches sometimes arise from the arch ; most commonly it is the left vertebral, 

 which usually takes origin between the left carotid and left subclavian, or beyond them. Some- 

 times a thyroid branch is derived from the arch, or the right internal mammary, or left vertebral, 

 or, more rarely, both vertebrals. 



THE CORONARY ARTERIES. 



The coronary arteries supply the heart ; they are two in number, right and left, 

 arising near the commencement of the aorta immediately above the free margin 

 of the semilunar valves. 



The R!,<jlit Coronary Artery, about the size of a crow's quill, arises from the 

 aorta immediately above the free margin of the right semilunar valve,, between 



