Are medicare tax and SS tax included as part of a given tax bracket percentage?

For example, in 2009 if you make between $33,950 and $82,250, and are filing as single, then you are in the “25% Tax Bracket”—but a lot of the time, on a W2, they’ll separate out “medicare” and “social security” withholdings as separate from “income tax withheld”.

So are the Medicare and Social Security a part of the total 25%, or are they withheld in addition to the 25%, meaning that you’re really paying greater than the 25% in the end??