What is the layer of peritoneum that attaches to the posterior wall of the abdominal cavity and connects to the small intestine?

The correct choice reflects the structure known as the mesentery, which is a crucial supporting structure in the abdominal cavity. The mesentery is a double layer of peritoneum that extends from the posterior abdominal wall to encase the small intestine. Its primary role is to anchor the small intestine in place while allowing for the necessary mobility during digestion.

The mesentery also contains blood vessels, nerves, and lymphatics that supply the intestines, ensuring they receive the nutrients and support they need to function effectively. This anatomical feature is essential for maintaining the integrity and organization of the abdominal cavity.

In contrast, the serosa is a smooth membrane that covers the outside of many abdominal organs, providing a frictionless surface. The term peritoneum refers to the entire serous membrane lining the abdominal cavity and surrounding organs, not exclusively to the layer that connects to the intestine. The omentum refers to structures that connect the stomach to other organs and do not serve the same function as the mesentery regarding the small intestine. Thus, the mesentery is distinctly responsible for connecting the small intestine to the posterior wall of the abdominal cavity, making it the correct answer.