Atrial veins of the human heart.

Modern anatomical description divides the cardiac veins into two groups: tributaries of the greater cardiac vascular system (GCVS) and tributaries of the smaller cardiac vascular system (SCVS), consisting of the Thebesian vessels. Both systems intercommunicate extensively. With the exception of the oblique vein of the left atrium (Marshall's vein), veins draining the walls of both the left and right atrium have not been well illustrated or described in anatomical atlases and textbooks. Consequently, we do not know exactly to which of the two groups (GCVS or SCVS) the atrial veins belong. There are three groups of left atrial veins: (1) tributaries of the left coronary vein and the coronary sinus; (2) special veins draining the right-sided walls of the left atrium that terminate via intramural sinuses in the right atrium, which vessels occur in 92% of cases and belong to the GCVS; (3) in 81% of cases special veins drain the myocardium of the posterior and superior walls of the left atrium. In most cases they empty into the left atrium itself; in almost 40% of the cases they are connected with mediastinal veins. These veins, also belonging to tributaries of the GCVS, constitute a distinctly separate category of cardiac veins and should be designated proper veins of the left atrium. The veins draining the walls of the right atrium fall also into three groups: (1) In most cases there are short or large intramural tunnels or sinuses in the basic walls of the auricle and atrioventricular node area. The generally valveless openings of all the venous tunnels and sinuses are lined up on a circle just above the tricuspid valve and between the openings of both venae cavae. (2) There are also thin veins at the junction of the right atrium with both the superior and inferior vena cava. (3) In addition, there are numerous cardiac veins of the "smallest size" (real Thebesian veins).