After the pericardium and pleurae have been separated off the remainder of the coelom becomes the peritoneum.
There is probably very little difference in the lower level of the pleurae on the two sides.
early 15c., medical Latin, from Greek pleura "side of the body, rib," also "flank of an army, page of a book," of unknown origin.
pleura pleu·ra (plur'ə)
n. pl. pleu·rae (plur'ē)
The thin serous membrane that envelops each lung and folds back to make a lining for the chest cavity.