In Animal Farm, how does Boxer fit into the exposition?

Boxer fits into the exposition established in the first
chapter because he represents everything that Old Major is discussing.  When Old Major
talks about how the animals' labor is being exploited by the humans, he is typifying the
condition of Boxer.  The old cart house is an impeccable worker, struggling for hours on
end with little, if anything, to show for all of his labor.  Old Major actually makes
pointed reference to this by saying that when Boxer has outlasted his usefulness, he
"will be sent to the Knacker's."  This condition is one where Boxer is a direct
reflection of Old Major's vision of how things are.  Boxer also serves as a direct
benefactor of Old Major's vision of how things will be under his idea of "Animalism." 
The idea of being able to be in a position whereby animals like Boxer will be able to
benefit from their labor is something that reflects Boxer because he will be able to
actually benefit from his extreme level of work and work ethic.  It is in this way where
the opening or exposition as articulated in Old Major's speech is something that
reflects Boxer's state of being in the farm.