The coronary arteries are small vessels, two in number, which arise near the root or commencement of the aorta, immediately above the semilunar valves. They are called coronary, from the manner in which they encircle the heart near its base, (corona, a wreath or garland). They have likewise been named cardiac, from their destination to the substance of that organ. The two arteries are distinguished as right and left coronary arteries from the direction they take, or from the sides of the heart which they respectively supply.
The right coronary artery (art. coronaria dextra), about the size of a crow's quill, is seen close to the right side of the pulmonary artery, between it and the right auricle. It arises from the aorta just above the free margin of the right semilunar valve, and runs obliquely towards the right side of the heart, lodged in the groove which sepa- rates the auricle from the corresponding ventricle. Having passed the right border of the heart, the vessel continues its course in the same way along the posterior aspect of the organ, until it reaches the groove of separation between the two ventricles, where it divides into two branches. One of these continues on transversely to the groove between the left auricle and ventricle, and anastomoses with the left coronary artery ; whilst the other branch, assuming a different course, runs longitudinally downwards along the posterior wall of the septum between the ventricles, and giving branches to each ventricle and to the septum between them, terminates at the apex of the heart by anastomosing with the descending branch of the left coronary artery, which is seen on the fore part of the inter-ventricular septum.
In its course, the right coronary artery, besides the offsets already noticed, gives small branches to the right auricle and ventricle, and also to the origin of the pulmonary artery. Along the right border of the ventricle a rather large branch usually descends towards the apex of the heart, and sends branches in its progress to the anterior and posterior surfaces of the ventricle.
The left coronary artery (art. cor. sinistra s. post.) is smaller than the preceding, and arises from the left side of the aorta higher up by a line or two. It passes behind and then to the left side of the pulmonary artery, appearing between that vessel and the left auricular appendage. At first it descends obliquely towards the sulcus, which separates the ventricles of the heart in front, where it divides into two branches. Of these, one continues to pursue a transverse direction, turning outwards and to the left side in the groove between the left ventricle and auricle, and after reaching the posterior aspect of the heart, anastomoses with the transverse branch of the right coronary- artery ; the other branch, much the larger, descends on the anterior surface of the heart along the line of the inter-ventricular septum towards the apex of the organ, and anastomoses with the long descending branch of the right coronary artery.
The left coronary artery supplies some small branches at its com- mencement to the pulmonary artery, to the coats of the aorta itself, and to the left auricular appendage; its two branches also furnish smaller offsets throughout their course, which supply the left auricle, both ventricles, and the inter-ventricular septum.
Peculiarities of the coronary arteries
The coronary arteries have been observed in a few instances to commence by a common trunk, from which they diverged and proceeded to their usual destination. The existence of three coronary arteries is not a very rare occurrence, the third being small and arising close by one of the others. Meckel, in one instance, observed four, the supplementary vessels appearing like branches of one of the coronary arteries transferred to the aorta.
From Quain's Anatomy.