|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|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 birththe 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-phrenics, and the superior and inferior epigastrics.|
Peculiarities.The height to which the aorta rises in the thorax is usually about 2.5 cm. below the upper border of the sternum; but it may ascend nearly to the top of the bone. Occasionally 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 occasionally 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