This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Posterior Or Descending Portion Of The Arch extends from the body of the second to that of the third dorsal vertebra: posteriorly, and at its right, it rests against the spine and left longus colli muscle; on its right side also are the oesophagus, thoracic duct, and vena azygos: anteriorly it is covered by the root of the left lung; and on its left side the left lung and pleura are situated. In these different stages, besides the various relations already enumerated, the artery is surrounded by a number of dark-colored bronchial glands : when these become enlarged by disease, to which they are very liable, they occasionally produce most serious effects by their pressure on the air-tubes, on the vena cava, and on the large arteries of the neck which they accompany.
Taking the entire of the arch of the aorta, we will find the following parts embraced within its concavity: first, the right pulmonary artery; second, that portion of the left auricle with which the appendix is connected; third, the left division of the trachea; fourth, the cardiac ganglion of Wrisberg; fifth, the ligamentous remains of the ductus arteriosus; sixth, the left recurrent nerve.
The arch of the aorta has important venous relations : we may observe the superior vena cava, when all the vessels are moderately filled, lying to the right side of the first stage of the arch, and the left vena innominata, lying above, and very near the upper margin of the second stage. The student would do well to attend to the anatomy of these venous trunks: he will perceive, after opening the pericardium, a large vein presenting a dark blue color, lying to the right of the aorta: this is the vena cava superior or descendens; it is covered, except at its most posterior part, by the serous layer of the pericardium: it is about three inches in length; it enters the fibrous layer of the pericardium, so that about one-third of the vessel is contained within this sac; and it is situated entirely within the thorax. It is formed chiefly by the confluence of the right and left venae inno-minatae, or brachio-cephalic veins : this union takes place about an inch and a half below the bifurcation of the arteria innominata, and corresponds anteriorly to the upper part of the second rib, near its articulation with the right side of the sternum. The vein descends nearly in a vertical direction, but slightly curved, the concavity being directed to the left, and corresponding to the right side of the first stage of the aorta; the convexity is to the right side. It here lies anterior to the right pulmonary vessels, and enters into the upper part of the right auricle behind the auricular appendix. The vena azygos enters the cava at its posterior surface, just before this large vein passes into the pericardium. The other veins which pour their blood into the superior cava, are, the right inferior thyroid and internal mammary veins, the thymic, pericardial, mediastinal, and right superior phrenic : these veins usually enter the vessel at its commencement, and in its extra-pericardial stage. In this stage the vein has numerous relations: behind it we observe the vena azygos, a portion of the trachea, the right vagus nerve, some lymphatic glands, and loose areolar tissue ; to the outside, we have the right phrenic nerve, the right pleura and lung; anteriorly, the remains of the thymus gland, some areolar tissue belonging to the anterior mediastinum, and the phrenic nerve; and to its left or inner side we have the arch of the aorta.
The arch of the aorta being in close relation both to the anterior and posterior walls of the chest, as well as to its interior, and being surrounded by numerous cavities and tubes, it is evident that an aneurismal tumor affecting this portion of the vessel may open in a great variety of situations. We frequently find it absorbing the sternum at its junction with the cartilage of the second or third rib of the right side, and pointing, or even opening, anteriorly. It has also been known to burst into the right auricle of the heart, into the pericardium, the pulmonary artery, the trachea, bronchial tubes, and air-cells; into the mediastinum, oesophagus, right and left pleurae, and into the spinal canal; also to press upon and obstruct the thoracic duct, or obliterate the subclavian or common carotid artery. In some cases the tumor ascends behind and above the clavicle, and simulates subclavian or carotid aneurism; in other cases its pressure anteriorly has been known to dislocate the clavicle, and the occurrence of dyspnoea, aphonia, and dysphagia during its progress can be accounted for by pressure on the air-passages, recurrent nerve, and oesophagus.
Mr. Smith has described a very remarkable case of aneurism of the ascending portion of the aorta, the front of which was divided by the pulmonary artery into two portions, one of which projected into the right ventricle, and the other into the left. From each of these cavities the sac was divided only by a very delicate membrane, that must have been absorbed had the patient lived a very little longer.*