In the developing heart, the valves between the atria and ventricles, the bicuspid and therefore the tricuspid valves, develop on either side of the atrioventricular canals. The canal becomes invaginated into the ventricle cavities by the extension of bases of the ventricles. The invaginated margins form the rudiments of the lateral cusps of the Atrioventricular valves. the center and septal cusps develop from the downward extension of the septum intermedium.