as you say the fox terrier was to play a vital role in the desighn of the jack as i belive they are a far older breed of dog .an you can still see obviouse sighns of them into todays russells .it is stated that russell didnt care for the looks of the dog as long as it worked to its job in hand. and he let his best dogs live in by the fire and sleep on his bed .later refrences have found this to be untrue although no one can take away his knoledge of yhe hunting world an the breeding of dogs of witch he claims he would never sell a dog. other claim he would have no complaints about breeding dog