I didn't know that they were once in a pub in Liverpool. I have seen them at the York Railway Museum. They are beautifully displayed.
As to Labradors it is because there were probably none around when the picture was painted. They are a very recent breed. The main dogs of the period would have been the Flat Coat Retriever for the Gentleman, the Curley Coat for the Wildfowler or Gamekeeper and the various Setters and Pointers for walked up grouse shooting over muzzle loaders and early breech loaders. Lagopus.....
