Magento - Proceed to Checkout button location in theme

I am looking to track down the file (and it's location) that generates the "Proceed to Checkout" button in the Magento cart.

Try adding a product to the cart, and then proceeding to the cart. The "Proceed to Checkout" button is on the right hand side of the cart.

I am using a hacked-about variation of the blank theme, if that makes any difference.

Thanks in advance for your help.