480 THE BLOOD-VASCULAR SYSTEM. 



Regarding the transverse aorta, 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 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 symptoms 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 oesophagus, producing 

 dysphagia ; or may burst into the oesophagus, when fatal haemorrhage will occur. Again, the 

 innominate artery, or the subclavian, or left carotid, 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 in the left tem- 

 poral artery ; or the tumor may present itself at or above the manubrium, generally either in the 

 median line or to the right of the sternum, and may simulate an aneurism of one of the arteries 

 of the neck. 



BRANCHES OF THE ARCH OF THE AORTA (Figs. 280, 281). 



The branches given off from the arch of the aorta are three in number : the 

 innominate artery, the left common carotid, and the left subclavian. 



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

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

 commencement 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 toward the innominate artery. 



The Number of the primary branches may be reduced to a single vessel, or more commonly 

 two : the left carotid arising from the innominate artery, or (more rarely) the carotid and sub- 

 clavian 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 has been found 

 to arise from the left end of the arch ; in other cases it was the second or third branch given off 

 instead of the first. Another common form in which there are four primary branches is that 

 in which the left vertebral artery arises from the arch of the aorta between the left carotid and 

 subclavian arteries. Lastly, the number of trunks from the arch may be increased to five 

 or six ; in these instances, the external and internal carotids arise separately from the arch, the 

 common carotid being absent on one or both sides. In some cases, where six branches have 

 been found, it has been due to a separate origin of the vertebral on both sides. 



Number Usual, 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. 1 



In some instances other arteries are found to arise from the arch of the aorta. Of these 

 the most common are the bronchial, one or both, and the thyroidea ima; but the internal 

 mammary and the inferior thyroid have been seen to arise from this vessel. 



INNOMINATE ARTERY. 



The innominate artery (brachio-cephalic) is the largest branch given off from 

 the arch of the aorta. It arises, on a level with the upper border of the second 

 right costal cartilage, from the commencement of the arch of the aorta in front 

 of the left carotid, and, ascending obliquely to the upper border of the right 

 sterno-clavicular articulation, divides into the right common carotid and right 

 subclavian arteries. This vessel varies from an inch and a half to two inches in 

 length. 



Relations. In front, it is separated from 'the first piece of the sternum by the 

 Sterno-hyoid and Sterno- thyroid muscles, the remains of the thymus gland, the 

 left innominate and right inferior thyroid veins which cross its root, and some- 

 times the inferior cervical cardiac branch of the right pneumogastric. Behind, it 

 lies upon the trachea, which it crosses obliquely. On the right side is the right 

 innominate vein, right pneumogastric nerve, and the pleura ; and on the left side, 



1 The anomalies of the aorta and its branches are minutely described by Krause in Henle's 

 Anatomy (Brunswick, 1868), vol. iii., p. 203 et seq. 



