Jack Dempsey's Dog

My school bus driver also owned the local hardware store. He was a good guy and knew me well enough at age 9 to address me when we met. His name was "Jack".
Jack owned a little terrier that raced alongside his truck as Jack drove to the hardware store.

Pulling out of his drive one day, Jack ran over his dog. Luckily, he didn't kill him .
But the dog's injury required a trip to surgery where his right rear leg had to be amputated.
Next thing I knew the dog was back chasing after Jack's truck as he went to work. If you didn't look closely you could never tell the dog only had three legs!

I don't think I ever knew the dog's name.
My friends and I called him 'The Arithmetic Dog"-
Because he "put down three, and carried one"!