"On leaving the right ventricle blood goes to the pulmonary artery. From the left ventricle, blood goes to the aorta; from the aorta there are branches to all parts of the body. The pressures in the pulmonary artery are about one-fifth those in the aorta and its branches; but the structure of the pulmonary artery is like that of arteries anywhere. The pulmonary circulation will be considered later"