Pull the other one, it's got bells on

Can someone help me with the ORIGIN of THIS expression?
I'm not looking for it's meaning, I know it's when someone doesn't believe what was said. I'm not looking for the origin of Pulling my leg either - just the phrase Pull The Other One, It's Got Bells On.
BTW - what is the connection between the bells and someone's leg? Doesn't seem relevant, just two expressions that got confused together.

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