This may be to a slight or to an extreme degree. In most cases the ventricular and auricular septa are also defective. (Kussmaul in 192 cases found the ventricular septum complete in only 21.) The most extreme case is that in which the pulmonary artery is entirely wanting, and the aorta receives the blood from both ventricles. In this case the lungs are supplied from the aorta by means of the Ductus arteriosus Botalli, which remains patent, the blood passing, however, in the reverse direction to that which obtains in the foetus. In its minor degrees stenosis of the pulmonary artery may be associated with a complete ventricular septum, but the foramen ovale is likely to remain open. Stenosis of the pulmonary artery leads to hypertrophy of the right ventricle just as a similar obstruction does in the adult.