This is from “Wit Restored” by John Mennes, dating to 1658:

On a Maid’s Leg

Fair Betty used to tuck her coats up high,
That men her foot and leg might soon espy.
Thou hast a pretty leg, (saith one) fair Duck.
Yea, two, (saith she) or else I have ill luck.
They’re two indeed, they’re twins, I think, quoth he,
They are, and yet they are not, Sir, said she;
Their birth was both at once, I dare be sworn
And yet between them both a man was born.