Having the form of the segment of a circle; being a segment: as, a segmental arch.Of or pertaining to segments or segmentation: as, a segmental formula; segmental parts; segmental organs.Specifically, in embryology, noting the primitive and rudimentary renal organs which occur in all vertebrates and some invertebrates, consisting in the former of branched tubules opening at one end into the somatic cavity and at the other by one or more main ducts into the cloaca or hindgut.