548 ANGIOLOGY 





arteriosum into the aorta. According to Bonnet 1 this coarctation is never found in the fetus or 

 at birth, and is due to an abnormal extension of the peculiar tissue of the ductus into the aortic 

 wall, which gives rise to a simultaneous stenosis of both vessels as it contracts after birth the 

 ductus is usually obliterated in these cases. An extensive collateral circulation is set up, by the 

 costocervicals, internal mammaries, and the descending branches of the transverse cervical 

 above the stenosis, and below it by the first four aortic intercostals, the pericardiaco-phrenks, 

 and the superior and inferior epigastrics. 



Peculiarities. The height to which the aorta rises in the thorax is usually about 2.5 era. 

 below the upper border of the sternum; but it may ascend nearly to the top of the bone. Occa- 

 sionally it is found 4 cm., more rarely from 5 to 8 cm. below this point. Sometimes the aorta 

 arches over the root of the right lung (right aortic arch) instead of over that of the left, and passes 

 down on the right side of the vertebral column, a condition which is found in birds. In such cases 

 all the thoracic and abdominal viscera are transposed. Less frequently the aorta, after arching 

 over the root of the right lung, is directed to its usual position on the left side of the vertebral 

 column; this peculiarity is not accompanied by transposition of the viscera. The aorta occa- 

 sionally divides, as in some quadrupeds, into an ascending and a descending trunk, the former 

 of which is directed vertically upward, and subdivides into three branches, to supply the head 

 and upper extremities. Sometimes the aorta subdivides near its origin into two branches, which 

 soon reunite. In one of these cases the esophagus and trachea were found to pass through the 

 interval between the two branches; this is the normal condition of the vessel in the reptilia. 



Branches (Figs. 505, 506). The branches given off from the arch of the aorta 

 are three in number: the innominate, the left common carotid, and the left subclavian. 



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

 part of the arch, may spring from the commencement of the arch or upper part of the ascending 

 aorta; or the distance between them at their origins 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 one, or more commonly 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 has been found to arise from the 

 left end of the arch; in other cases it is 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 few cases six branches have been found, and this condition is associated 

 with the origin of both vertebral arteries from the arch. 



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 artery is a left 

 one, and the right carotid and subclavian arise separately. 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. 



In some instances other arteries spring from the arch of the aorta. Of these the most common 

 are the bronchial, one or both, and the thyreoidea ima; but the internal mammary and the inferior 

 thyroid have been seen to arise from this vessel. 



The Innominate Artery (A. Anonyma; Brachiocephalic Artery) (Fig. 505). 



The innominate artery is the largest branch of the arch of the aorta, and is from 

 4 to 5 cm. in length. It arises, on a level with the upper border of the second 

 right costal cartilage, from the commencement of the arch of the aorta, on a plane 

 anterior to the origin of the left carotid; it ascends obliquely upward, backward, 

 and to the right to the level of the upper border of the right sternoclavicular 

 articulation, where it divides into the right common carotid and right subclavian 

 arteries. 



Relations. Anteriorly, It is separated from the manubrium sterni by the Sternohyoideus and 

 Sternothyreoideus, the remains of the thymus, the left innominate and right inferior thyroid veins 

 which cross its root, and sometimes the superior cardiac branches of the right vagus. Posterior 



1 Rev. de M6d., Paris. 1903. 



