Figure 14.

This section, from a human embryo at Carnegie stage 20, just subsequent to the completion of ventricular septation, shows how the leaflets of the tricuspid valve are delaminating within the part of the primary heart tube from which ballooned the apical component of the right ventricle. As the leaflets delaminate from the superficial layers of ventricular myocardium, they incorporate the endocardial cushions within their substance, subsequently being transformed into fibrous tissue.