As viewed from the right atrium, the floor of the fossa ovalis is formed by: (A) Septum primum, (B) Septum secundum, (C) Endocardial cushions, (D) Tricuspid valve orifice
Answer is A. Fossa oavlis represents the site of embryonic spectum primum hence from right atrium its seems to be developed from septum primum. BD CHAURASIA'S HUMAN ANATOMY.VOLUME 1. 6TH EDITION.PAGE NO 255