THE INNOMINATE ARTERY. 545 



been reported to. from the supposition that disease existed in the larynx ; or it may press up.on 

 the thoracic duct and destroy lite by inanition ; or it may involve the oesophagus, producing 

 dysphairia : 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. 



t 



BRANCHES OF THE ARCH OF THE AORTA (Figs. 344, 345). 



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 

 : being the approximation of the left carotid toward the innominate artery. 



Tin J\ n mix / 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 aris- 

 inir 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. 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. 



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

 the three brandies 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 

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

 and the sulclavians 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 such a secondarv 

 branch is the left vertebral, which usually takes origin between the left carotid and left subcla- 

 vian. or beyond them. Sometimes, a thyroid branch is derived from the arch, or the right 

 internal mammary, or right vertebral, or. more rarely, both vertebral. 1 



THE INNOMINATE ARTERY. 



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

 the arch of the aorta, It arises opposite the fourth dorsal vertebra 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 bone of the sternum by the 

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

 left innominate and right inferior thyroid veins which cross its Yoot, 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, 

 the remains of the thymus gland, the origin of the left carotid artery, the left 

 inferior thyroid vein, and the trachea. 



Branches. The innominate usually gives off no branches, but occasionally a 

 small brunch, the thyroidea ima, is given off from this vessel. It also sometimes 

 gives off a thymic or Irom-hiid. launch. The Thyroidea ima ascends in front of 

 the trachea to the lower part of the thyroid body, which it supplies. It varies 

 greatly in size, and appears to compensate for deficiency or absence of one of the 

 other thyroid vessels. It occasionally is found to arise from the subclavian or 

 internal mammary vessel. 



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. 



