Therightmarginopensintothegreatersacthroughtheopeningofthelessersacorepiploicforamen. The opening into the lesser sac (epiploic foramen) has the following boundaries: Anteriorly: Free border of the lesser omentum, the bile duct, the hepatic artery, and the portal vein. Posteriorly: Inferior vena cava. Superiorly: Caudate process of the caudate lobe of the liver. Inferiorly: First part of the duodenum. Sagittal section through the entrance into the lesser sac showing the important structures that form boundaries to the opening.