TWO FOR TUESDAY - MIDSOMER RADIO (PART TWO)

'MIDSOMER MURDERS'
"TALKING TO THE DEAD"

At the scene of a murder, a radio was found blaring a radio adaptation of Euripedes' "Medea".  The actress heard playing the role is Claire Higgins, known for the "Hellraiser" movies and as the High Priestess Ohila in a small 'Doctor Who' online movie featuring Paul McGann as the Eighth Doctor.

Later, while DCI Tom Barnaby is investigating, he turns the radio back on.  By this time, the programming is now a variety show where Barnaby hears this hoary old chestnut:

'I thought you said your dog didn't bite .' 
'Whose dog?' 
'Your dog.' 
'Yeah. But that's not my dog.'

I'm not sure what the genesis for this joke is, but I've found it in two novels:

"Quirkology: How We Discover the Big Truths in Small Things"
by 
Richard Wiseman

"Eye Opener"
by
Michael Z. Lewin 

"Manitou Canyon: A Novel"
by
William Kent Krueger 

Krista Procklw used the joke as the opening ice-breaker in an article about "Dog Liability in British Columbia".

A man walks into a bar and sits down
next to a woman with a dog at her feet.
“Does your dog bite?,” he asks. “No.”
A few minutes later, the dog takes a huge chunk
out of the man’s leg.
“I thought you said your dog didn’t bite!” he says indignantly.
“That’s not my dog” , replies the woman. 

And of course there is the most famous iteration of the joke from the movies:

So....  Does anybody know where the joke started?