<Li> The peritoneum is the serous membrane that surrounds several organs in the abdominopelvic cavity . </Li> <P> The serous fluid produced by the serous membranes reduces friction between the walls of the cavities and the internal organs when they move, such as when the lungs inflate or the heart beats, that could otherwise lead to inflammation of the organs . </P> <P> The serous membranes have two layers, parietal and visceral, surrounding a fluid filled space . </P> <P> All serous membranes found in the human body formed ultimately from the mesoderm of the trilaminar embryo . The trilaminar embryo consists of three relatively flat layers of ectoderm, endoderm (also known as "entoderm") and mesoderm . </P>

Which term describes the structure that separates the thoracic cavity from the abdominal cavity