The human body possesses two large cavities (pleural and peritoneal) and a smaller cavity (pericardial), all of which are covered with a mesothelium. One speaks of visceral mesothelium that coats the organs and parietal mesothelium that coats the somatic walls delimiting the cavitiy towards the inside and also the outside.
Origin of the pleural cavities
In stage 10 (28 days) the cranial section of the intraembryonic coelom consists of a middle part, the pericardial cavity, and two thin canals laterally, the pericardioperitoneal canals.
They connect the pericardial cavity with the part of the intraembryonic coelom that is open towards the outside, the future peritoneal cavity. At this point no pleural cavity yet exists because the lungs have not yet begun to develop.
In stage 13 (32 days), the lung buds grow into the pericardioperitoneal canals and dent them. Thereby the pericardioperitoneal canals are subdivided on both sides by these lung buds that are sprouting in from the medial direction.
With the increase in size of the lung anlage the pericardioperitoneal canal widens to become the pleural cavity that is separated from the pericardial cavity by the pleuropericardial membrane and from the peritoneal cavity by the pleuroperitoneal membrane.
In the region of the peritoneal cavity and the umbilical coelom, the left and right peritoneal tubes join ventrally to form a common cavity, the peritoneal cavity, that goes over into the umbilical coelom. In the dorsal region they form the meso of the guts.
The lungs become covered by the visceral layer of the pleural cavity, the pleura visceralis. Towards the outside, the pleural cavity is bounded by the parietal layer, the pleura parietalis. Through their rapid increase in size the two lungs, left and right, enclose the heart that is in their middle.
In the following interactive diagram (development of the pleural cavity in various stages) the intraembryonic coelom can be seen in various stages. One distinguishes the pericardial cavity in the middle from the two pleural cavities and, in the intestinal region, the peritoneal cavity.