As the lung grow downwards the mesoderm of the lateral body wall between them and liver is stripped off, forming a ridge at the caudal end of each pleural cavity. These ridges project into the lateral aspect of pleuroperitoneal openings and each of them now called as a pleuroperitoneal membrane. As these membranes grow and extend medially, each of them ultimately fuses with the septum trans-versum ventral to the foregut. More dorsally, the pleuroperitoneal membranes fuse with the dorsal mesentery of the foregut.