单项选择题
A．It is located in the middle mediastinum B．It can be divided into fibrous and serous pericardium C．It encloses the heart D．It forms a closed cavity called pericardial cavity E．It attaches to the visceral pleura
A．right atrium B．superior vena cava C．inferior vena cava D．right ventricle E．left atrium
A．a foramen between the right atrium and the left one B． existent during the fetus C．located on the lower part of the right surface of the interatrial septum D．the thickest part of the wall of the heart E．a remnant of the fetal heart between the atrium and ventricle