It is composed of a layer of serous membrane fused with a layer of mucus membrane. ??? ??? ??? All of the following organs are retroperitoneal except the duodenum. ??? ??? ??? Which of the following arteries is not a branch of the celiac trunk? the hepatic portal track ??? ??? ??? Which of the following is the most common cause of peritonitis? burst appendix ??? ??? ??? Particularly large collecti