Pleuroperitoneal and pleuropericardial canals are not defined. The ventral mediastinal pleura is thus the pleura on the dorsal aspects of these folds. Costal pleura is enclosed dorsally by the developing ribs.
Diaphragmatic pleura covers the superior surface of the pleuroperitoneal folds.
During this stage the pleuro-pericardial canals close and the mediastinal pleura are completed. The costal pleura reach down as far as the seventh ribs but the pleural sacs are still retrocardiac. The pleura encircle the dorsal half of the pericardium and extend from the second to the ninth ribs. The pleura that cover the suprarenal, gonadal glands and mesonephroi, dips behind the glands, following the diaphragm.