The membrane that holds the coils of the small intestine is called the mesentery. The mesentery is a double-layered sheet of tissue that attaches the small intestine to the posterior abdominal wall. It contains blood vessels, lymph vessels, and nerves that supply the small intestine and also contains fat, the omentum, which acts as a cushion and protects the organs in the abdomen. The mesentery also helps to keep the coils of the small intestine in place, allowing for efficient mixing and movement of food as it is digested.