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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
which it is continued to the apex of the heart as the posterior descending branch. It gives off a large marginal branch which follows the acute margin of the heart and supplies branches to both surfaces of the right ventricle. It also gives twigs to the right atrium and to the part of the left ventricle which adjoins the posterior longitudinal sulcus.
  The Left Coronary Artery (a. coronaria [cordis] sinistra), larger than the right, arises from the left anterior aortic sinus and divides into an anterior descending and a circumflex branch. The anterior descending branch passes at first behind the pulmonary artery and then comes forward between that vessel and the left auricula to reach the anterior longitudinal sulcus, along which it descends to the incisura apicis cordis; it gives branches to both ventricles. The circumflex branch follows the left part of the coronary sulcus, running first to the left and then to the right, reaching nearly as far as the posterior longitudinal sulcus; it gives branches to the left atrium and ventricle. There is a free anastomosis between the minute branches of the two coronary arteries in the substance of the heart.

Peculiarities.—These vessels occasionally arise by a common trunk, or their number may be increased to three, the additional branch being of small size. More rarely, there are two additional branches.

The Arch of the Aorta (Arcus AortÆ; Transverse Aorta) (Fig. 505).—The arch of the aorta begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta. It thus forms two curvatures: one with its convexity upward, the other with its convexity forward and to the left. Its upper border is usually about 2.5 cm. below the superior border to the manubrium sterni.

Relations.—The arch of the aorta is covered anteriorly by the pleuræ and anterior margins of the lungs, and by the remains of the thymus. As the vessel runs backward its left side is in contact with the left lung and pleura. Passing downward on the left side of this part of the arch are four nerves; in order from before backward these are, the left phrenic, the lower of the superior cardiac branches of the left vagus, the superior cardiac branch of the left sympathetic, and the trunk of the left vagus. As the last nerve crosses the arch it gives off its recurrent branch, which hooks around below the vessel and then passes upward on its right side. The highest left intercostal vein runs obliquely upward and forward on the left side of the arch, between the phrenic and vagus nerves. On the right are the deep part of the cardiac plexus, the left recurrent nerve, the esophagus, and the thoracic duct; the trachea lies behind and to the right of the vessel. Above are the innominate, left common carotid, and left subclavian arteries, which arise from the convexity of the arch and are crossed close to their origins by the left innominate vein. Below are the bifurcation of the pulmonary artery, the left bronchus, the ligamentum arteriosum, the superficial part of the cardiac plexus, and the left recurrent nerve. As already stated, the ligamentum arteriosum connects the commencement of the left pulmonary artery to the aortic arch.
  Between the origin of the left subclavian artery and the attachment of the ductus arteriosus the lumen of the fetal aorta is considerably narrowed, forming what is termed the aortic isthmus, while immediately beyond the ductus arteriosus the vessel presents a fusiform dilation which His has named the aortic spindle—the point of junction of the two parts being marked in the concavity of the arch by an indentation or angle. These conditions persist, to some extent, in the adult, where His found that the average diameter of the spindle exceeded that of the isthmus by 3 mm.
  Distinct from this diffuse and moderate stenosis at the isthmus is the condition known as coarctation of the aorta, or marked stenosis often amounting to complete obliteration of its lumen, seen in adults and occuring at or near, oftenest a little below, the insertion of the ligamentum

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