<prompt> As viewed from the right atrium, the floor of the fossa ovalis is formed bySeptum primumSeptum secundumEndocardial cushionsTricuspid valve orifice  <response>: Fossa oavlis represents the site of embryonic spectum primum hence from right atrium its seems to be developed from septum primum. BD CHAURASIAS HUMAN ANATOMY.VOLUME 1. 6TH EDITION.PAGE NO 255 