Metonymy

Naming one thing by another connected to it: the part for the whole, the object for its owner, the place for the people, the cause for the effect.

In Don Quixote

I am Ginés de Pasamonte, whose life is written by these thumbs.

The "thumbs" stand for the hands that write, and the choice of the thumb, said by a man whose hands are bound, makes writing an act of the body and his life a text he himself drafts.

Part One: The Galley Slaves and the Sierra, Ginés de Pasamonte, the last galley slave on the chain

and so, considering this, I am inclined to say that in my soul I regret taking up this exercise of knight-errantry in an age as detestable as the one we now live in; because, although no danger frightens me, it does worry me to think whether gunpowder and lead will take from me the chance of making myself famous and known through the valor of my arm and the edge of my sword.

Part One: The Arms and the Captive, Don Quixote, at the inn table, in the speech on arms and letters