Subject: How do the tongue muscles function?

How do the tongue muscles function?
My understanding is that muscles only contract.  When you extend
your arm, it's because of the action of contracting muscles anchored
against the bone straightening out your arm.  When you bend
it, a different set of muscles is contracting to move your arm the
other way.
  So how do the muscles in your tongue act (by contracting) in order
for you to extend your tongue?  Also, is tongue curling caused by
muscle fibers lying "crosswise" on your tongue contracting? 

Re:How do the tongue muscles function?