Schematic diagram of murine PPM development.
(A–D) Scheme of PPM development based on transverse sections through the cardiac venous pole of wildtype embryos from E11.5 to E14.5. The lumen of the caval veins and the heart is marked in pale pink, the lung and trachea in pale blue, the (parietal) pleura in blue, the (parietal) pericardium in red, and the degenerating subcoelomic mesenchyme in green. Blue arrows demonstrate the direction of the detachment of the PPMs from the subcoelomic mesenchyme. Note the PPMs are double-layered consisting of the parietal layer of the pleura and the pericardium. Dorsal is up, ventral is down. h, heart; lu, lung; pc, pericardial cavity; pl, pleural cavity; ppc, pericardioperitoneal canal; ppm, pleuropericardial membranes.