secondarily developed vein in the wings of insects (T-B, after Comstock and Kellogg); an extra branch of a longitudinal vein (Borror et al.); in adult Symphyta (Hymenoptera), the most posterior vein in the anal area of the forewing, i.e., the third anal vein (A3) (Borror et al.; Riek, in CSIRO); see intercalary vein.