This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Lower one fouh of vagina is formed from: 
Select and explain. 
A. Urogenital sinus, B. Paramesonephric duct, C. Mesonephric duc, D. Mullerian duct
A: Urogenital sinus
Answer: A: Urogenital sinus 
Explanation: Uterovaginal canal (mesoderm) comes in contact with the urogenital sinus (endoderm). Sinovaginal bulbs are formed by the proliferation of endodermal lining. Solid vaginal plate is derived paly from mesoderm of uterovaginal canal and paly from endoderm of sinovaginal bulbs. Vagina is formed by canalization of vaginal plate. Lower one fouh of vagina is formed from urogenital sinus. Ref: Snell's, Clinical Anatomy, 7th Edition, Page 404; Human Embryology, 7th Edition, Page 283.