Pleura is a thin covering that protects and cushions the lungs. The pleura is made up of two layers of tissue that are separated by a small amount of fluid. Peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom- Perichondrium is a layer of dense, irregular connective tissue which surrounds, the cartilage of developing bone. Pericardium is a thin membrane that surrounds the heart and the roots of the great blood vessels.