The processes which are involved in the development of the normal outflow tracts of the ventricles are the following: The ostium bulbar torsion accounts for the concordant flow between the ventricles and the proximal conuses. The leftward shift of the ostium bulbi accounts for the partial overriding of the aorta over the left ventricle. The truncal rotation accounts for the twisted relationships of the great vessels and for the definitive interrelationships of the semilunar valves. The aortic conus absorption accounts for the aorticomitral fibrous continuity. These processes are not necessarily linked to each other. In the normal, mature heart the conus is represented by the subpulmonary portion of the right ventricular outflow tract.