What metaphors are used in The Life and Opinions of Tristram Shandy by Laurence Sterne?

In Volume Four, the only relevance of the Slawkenburguis story is that it continues from his father's discourse on noses. The story itself is pointless, but Tristram tells it with such suggestion of metaphor, the reader searches for meaning. What does Slawkenburguis's tale have to do with Tristram's nose? It provokes many different thoughts, but really it is just another digression and, if anything, proves the narrator's need to say what he likes. If there is any meaning, it is that Tristram is trying to imitate his Uncle Toby and his Father because they continually digress in their discussions. In fact, with Tristram making so few appearances, the reader can see this novel as homage to his two close relatives, and Tristram's opinions and digressions are just part of the respect.