urogenital sinus

https://doi.org/10.1351/goldbook.11345

Embryonic structure that forms in the ventral part of the cloaca when it separates from the anal canal to give rise to the genitourinary organs.

Note: A rare urogenital sinus anomaly occurs as a birth defect in the female when the urethra and vagina open into a common channel.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 817 (https://doi.org/10.1515/pac-2015-1202)