adult midgut constriction adult midgut constriction R2-R3 2014-06-05T17:29:32Z FBbt:00110916 fly_anatomy.ontology boundary R2-R3 BR2-R3 One of the two large constrictions of the adult midgut. It corresponds to an area where the midgut abruptly folds and turns up. It is the most ventral point of the midgut. The area is composed of a range of enterocytes with distinct identities. It separates region 2 (R2) from region 3 (R3).