Left and right ventricular trabecular patterns. Consequence of ventricular septation and valve development.

Study of serial sections of human embryos ranging from 3.6 to 25 mm crown rump length shows that the ventricular septum develops from three sources. The primary septum develops between the inlet and outlet which are the two first discernible segments of the ventricular portion of the primary heart tube. Two other septa develop within the inlet and within the outlet, respectively. Before and during septation all ventricular trabeculations are identical. In later stages, the atrioventricular valves and their tension apparatus develop from the inner myocardial layer of the left and right ventricular inlet parts. The outlet trabeculations do not take part in this process. These observations are suggested to explain the typical trabecular patterns of the apices of the mature left and right ventricles, which develop from the inlet and from the outlet, respectively.