Arterial vascularization of the sinuatrial node in the embryonic rat heart.

We studied the embryological development of the extracoronary cardiac vessels, determining their origins, courses and terminations in embryonic rat hearts. The sinuatrial node is supplied by an extracoronary artery, which can originate from (a) the right internal mammary artery, as a nodal artery, based on its origin; (b) the internal mammary artery, or (c) the right subclavian artery as a collateral artery of the cardiac branch of the cardiomediastinal trunk. The intimate relations of the nodal artery with the sinus node make it possible to study, at the same time, the development of the sinuatrial node in the rat embryo. The sinuatrial node always develops before the nodal artery, which does not appear until 16 or 16.5 days of development.