What are the flaps on the front of the atria called

Compare the lunar phase of the waning crescent to the waxing gibbous. the waning crescent is increasing in illumination and the waxing gibbous is decreasing in illumination. the waning crescent is decreasing in illumination and the waxing gibbous is increasing in illumination. the waning crescent is more than half illuminated and the waxing gibbous is less than half illuminated. the waning crescent is more than half illuminated and the waxing gibbous is more than half illuminated.