Morphogenesis of the venous valves in the rat heart. I. Light and scanning electron microscopy.

Hearts from rat embryos ranging from 12.5 days gestation through birth were studied with light and scanning electron microscopy. Both valves of the sinus venosus are very prominent structures in the right atrium of the developing rat heart. The right venous valve is large and undulating and extends to the right atrioventricular canal. Many nodules are apparent on the surface of this valve by the thirteenth day. These nodules decrease in number as development progresses. The left venous valve is considerably smaller than the right. Neither valve shows signs of regression, and just prior to birth, both valves are very prominent. The right valve is so large that it almost divides the right atrium into two chambers. Based on these observations the rat may serve as a model for cor triatriatum dexter.