primary urethral groove primary urethral groove the primary urethral groove or urethral groove is a temporary linear indentation on the underside (ventral side) of the male penis during embryonic development. primary urethral groovedetailsprecursorurogenital foldsgives rise tourethraidentifierslatinsulcus urethralis primariusteurethral groove_by_e5.6.4.2.1.7.3 e5.6.4.2.1.7.3 anatomical terminology in humans, it typically appears around 8 weeks of gestation and becomes closed into a normal male urethra by the 12th week. clinical significance failure of complete closure can be associated with hypospadias.