Vessels and Nerves of the Heart
The arteries. The two coronary arteries arise from the right and left sinuses of the aorta. The right coronary artery [a. coronaria dextre] passes forward between the pulmonary artery and the right atrium, and then follows the right coronary sulcus to the diaphragmatic surface of the heart, to anastomose with the left coronary artery. The posterior descending branch [ramus descendens posterior] arises at the posterior longitudinal sulcus. It easses in the furrow between the ventricles toward the apex, near which it anastomoses with ranches derived from the left coronary artery. In this course the right coronary artery supplies branches to the right atrium and roots of the pulmonary artery and aorta, as well as one that descends near the margo acutus (right marginal), and a second (preventricular) to the anterior wall of the right ventricle. It supplies both ventricles and the septum.
The left coronary artery [a. coronarius sinistra] passes for a short distance forward, between the pulmonary artery and the left auricle, and then divides into two principal branches, one of which runs in the anterior longitudinal sulcus to the apex of the heart, the anterior descending branch [r. descendens anterior], around which it sends branches to anastomose with the right coronary; whilst the other, the circumflex [ramus circumflexus], winds to the diaphragmatic surface in the coronary groove, to anastomose with the corresponding twigs of the right artery. In this course it gives off a branch which follows the margo obtusus (left marginal) as well as smaller branches to the left atrium, both ventricles, and the commencement of the aorta and pulmonary vessels.
The cardiac or coronary veins accompany the coronary arteries and return the blood from the walls of the heart.
The great cardiac vein [v. cordis magna], runs in the anterior longitudinal sulcus, passing round the left side of the heart in the coronary sulcus to terminate in the commencement of the coronary sinus. Its mouth is usually guarded by two valves, and it receives in its course the posterior vein of the left ventricle, with other smaller veins from the left atrium and ventricle, all of which are guarded by valves.
The middle cardiac vein (v. cordis media], sometimes the larger of the two chief veins, communicates with the foregoing at its commencement above the heart's apex. It ascends in the posterior longitudinal groove, receiving blood from the ventricular walls, and joins the coronary sinus through an orifice guarded by a single valve, close to its termination.
The posterior vein of the left ventricle [v. post, ventriculi sinistri], lies upon the posterior surface of the ventricle and, receiving branches from it, passes upward to terminate directly in the coronary sinus.
The anterior cardiac veins [vv. cordis anteriores] consist of several small branches from the front of the right ventricle, which vary in number and either open separately into the right atrium or join the lesser cardiac vein.
The small cardiac vein [v. cordis parva] is a small vessel which receives branches from both the right atrium and ventricle, and winds around the right side of the heart, in the coronary sulcus, to terminate in the coronary sinus.
The coronary sinus [sinus coronarius] may be regarded as a much-dilated terminal portion of the great cardiac vein. It is about 2.5 cm. (1 in.) in length, is covered by muscular fibers from the atrium, and lies in the coronary sulcus below the base of the heart. Its cardiac orifice, with the coronary (Thebesian) valve, has already been described. Besides the tributary veins already named, a small oblique vein [v. obliqua atrii sinistri] of the left atrium may sometimes be traced, on the back of the left atrium, from the ligament of the left vena cava (Marshall) to the sinus. This little vein, which is not always pervious or easy of demonstration, never possesses a valve at its orifice, and, Uke the coronary sinus, formed a part of the left superior vena cava of early fetal life.
The smallest cardiac veins [vv. cordis minima;] drain blood from septum and lateral walls of the atria, particularly the right; also from the conus arteriosus. They open directly into the right atrium.
Although anastomoses occur between the two coronary arteries, these are by no means extensive, and are not sufficient to allow of the establishment of a satisfactory collateral circulation in the case of the blocking of one coronary artery. Consequently, such interference with the cardiac circulation produces rapid pathological changes in the heart musculature, provided it is sudden in occurrence. If the obliteration of the artery take place gradually, however, some relief may be afforded by the establishment of a collateral circulation through the venae minimae, which open out from both the atrial and ventricular cavities and communicate with the finer branches of the cardiac veins, and also with the general capillary network in the heart's walls.
The lymphatic vessels of the heart pass chiefly through the anterior mediastinal lymph- nodes into the broncho-mediastinal trunk.
The cardiac nerves, derived from the vagus and the cervical sympathetic, descend into the superior mediastinum, passing in front of and behind the arch of the aorta; they unite in the formation of the superficial and deep cardiac plexuses. The superficial plexus lies above the right pulmonary artery as the latter passes beneath the aortic arch. The deep plexus lies between the trachea and the arch of the aorta, above the bifurcation of the pulmonary trunk. For the connections of the plexuses see section on Nervous System.