Caesarean section. The underlying rectus abdominis muscles and transversalis fascia will soon be divided to expose the peritoneal cavity. The peritoneum is composed of two membranes which line the inside of the abdominal cavity (parietal layer) and the internal organs (visceral layer). They contain a thin layer of fluid between them. They are required to minimise the friction between the internal organs and the surrounding wall during everyday activities. The fluid acts as a lubricant between the two layers.