Final answer:
The orifice allowing fetal blood to pass from the right atrium to the left in the fetal heart is called the foramen ovale, which closes after birth as the baby begins to breathe on their own.
Step-by-step explanation:
The name of the orifice that allows fetal blood to pass directly from the right atrium to the left in the fetal heart is the foramen ovale. During fetal development, the foramen ovale functions as a shunt to permit blood to bypass the non-functioning lungs.
After birth, the pressure changes in the heart cause the foramen ovale to close as a baby starts to breathe on their own and the lungs begin to function. The fossa ovalis is what remains as a marker of the former foramen ovale.
Other fetal circulatory structures include the ductus arteriosus, which connects the pulmonary trunk to the aorta, and the ductus venosus, allowing oxygenated blood from the placenta to bypass the fetal liver and go directly to the heart. These structures close after birth as part of the normal transition to postnatal circulation.