midgut Middle subdivision of a digestive tract[CJM]. In vertebrates: The middle part of the alimentary canal from the stomach, or entrance of the bile duct, to, or including, the large intestine[GO]. In humans: originates from the foregut at the opening of the bile duct into the duodenum and continues through the small intestine and much of the large intestine until the transition to the hindgut about two-thirds of the way through the transverse colon. That part of the alimentary canal which lies between the gizzard and the hind intestine. mesenteron subdivision of digestive tract