Which group of digestive structures lies wholly or partly behind the peritoneum?

1. A structure is called retroperitoneal when it sits behind the peritoneum rather than inside the peritoneal cavity. 2. During fetal development the duodenum, the pancreas and parts of the large intestine stay behind the peritoneum. 3. The parts of the large intestine that stay behind are the ascending colon, the descending colon and the rectum. 4. So the group of duodenum, pancreas, ascending colon and rectum is entirely retroperitoneal. 5. The jejunum and ileum are tethered by the mesentery inside the cavity, so that option is wrong. 6. The transverse and sigmoid colon hang from the mesocolon, so any option naming them is wrong. 7. The stomach hangs from the lesser and greater omenta, so it is not retroperitoneal either. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 23 "The Digestive System", section 23.1 Overview of the Digestive System_