Final answer:
The pubococcygeus muscle surrounds the vagina acting as a sphincter, and the vagina is related anteriorly to the bulb of the vestibule.
Step-by-step explanation:
Part of the pubococcygeus muscle surrounds the vagina about 3 cm above its opening into the vestibule and acts as a sphincter. Below this, the vagina is related anteriorly to the bulb of the vestibule and bulbospongiosus muscles.