I just googled "vagina plural" and it's either vaginas or vaginae. So I guess you get to pick which one you want to say by how much you want to pay.
Anyway they only found the vagina in about 1675 according to that source. So I don't know what you guys were screwing before then and I don't want to know.
And:
vagina ten·di·nis definition
Pronunciation: /-ˈten-də-nəs/
Function: n
: the synovial sheath of a tendon especially of the hand or foot
who would have thunked it?
You are all very welcome for this enlightenment.