"4th week: the septum primum, a muscular ridge with a mesenchymal cap originates at the posterior and superior atrial roof and grows towards the atrioventricular canal, lined by endocardial cushions; the ostium primum between the mesenchymal cap of the septum primum and the atrioventricular canal shrinks in this process."
"5th week: secondary perforations of the septum primum develop, just before the closure of the ostium primum at the time when the mesenchymal cap and vestibular spine fuse with the atrioventricular endocardial cushions; later the perforations expand and form the ostium secundum."
"8th-12th week: the mesenchymal cap and the vestibular spine differentiate into a myocardial rim or buttress at the anteroinferior border of the foramen ovale; an atrial infolding develops at the posterosuperior atrial roof just to the right atrial side of the septum primum."
"after birth: due to the increase of left atrial pressure, the flap-like septum primum is pushed against the posterosuperior right atrial fold and fuses with it."
Expected headings
"Relations and/or boundaries"
"Echocardiography"
"The interatrial groove is immediately adjacent to the atrial septum superiorly, posteriorly and inferiorly. Additional bordering structures include the following 1,2:"
"4th week: the septum primum, a muscular ridge with a mesenchymal cap originates at the posterior and superior atrial roof and grows towards the atrioventricular canal, lined by endocardial cushions; the ostium primum between the mesenchymal cap of the septum primum and the atrioventricular canal shrinks in this process."
"5th week: secondary perforations of the septum primum develop, just before the closure of the ostium primum at the time when the mesenchymal cap and vestibular spine fuse with the atrioventricular endocardial cushions; later the perforations expand and form the ostium secundum."
"8th-12th week: the mesenchymal cap and the vestibular spine differentiate into a myocardial rim or buttress at the anteroinferior border of the foramen ovale; an atrial infolding develops at the posterosuperior atrial roof just to the right atrial side of the septum primum."