Describe symbolism in The Crossing by Cormac McCarthy

The dog is a symbol for what the boys have lost in their lives, as well as an important part of the epiphany ending of the book. Throughout the book, the dog's presence presence is accepted without much interest. The boys occasionally feed him, but when they are riding hard and long across country, the dog trots along with the boys seeming to pay little attention. When Boyd is shot, the dog goes to his side and remains there.