What breed of dog is the dog in the Thin Man movies Asta?

Answer 1

In the Dashiell Hammett stories the Thin Man's dog was a female Schnauzer called Asta. They kept the name because the stories were so popular but the best dog star at the time was a male Wire Fox named Skippy. So he became Asta.

Answer 2

Asta was not a Jack Russell Terrier. He was a Wire-Haired Fox Terrier.

http://en.wikipedia.org/wiki/Skippy_%28dog%29