part_of starts_at ends_at urogenital sinus primitive bladder-caudal urogenital sinus transition zone EMAPA:36096 anatomical_structure primitive bladder-caudal urogenital sinus junction The primitive bladder-caudal urogenital sinus transition zone (syn: primitive bladder-caudal urogenital sinus junction) (TS:19-TS:21) is comprised of epithelium and mesenchyme of primitive bladder-caudal urogenital sinus transition zone. The zone or region where the primitive bladder meets the caudal urogenital sinus, marking the junction where these two different epithelia meet. It is similar to transitional zones in other organs, such as the female cervix and the Z-line in the oesophagus. In early developmental stages it is identified by the site of the common nephric duct/nephric duct attachment to the urogenital sinus. Part of the urogenital sinus. Use these terms to annotate expression in the epithelium or mesenchyme where the primitive bladder meets the caudal urogenital sinus/pelvic urethra, when the tissue cannot be identified as being either part of the bladder or part of the urethra. TS19 TS21