That "leg over" thing

I originally posted this a few days ago, but no reply, so giving it another go:
"Getting a leg over", meaning having sexual relations, is nice and visual -- but when did the phrase originate?

Sorry to report that I don't know any more about it than I did a few days ago. You might try a regional slang dictionary. This isn't a familiar phrase to me in the U.S.

It's quite commonly used in Australia, but what I do know is that we can't claim the err 'credit' for it. It's originally an English saying, but other than that I don't know it's origins. Still, as you suggest, it does paint something of a picture though.