We just learned about the Depressor Lip Muscles.
There are three muscles in your cheek area that help you do things like smile and whistle:
Orbicularis oris, risorius, and buccinator.
(from: wikipedia - Orbicularis oris muscle)
(from: wikipedia - risorius)
(from: wikipedia - buccinator muscle)
Kid Facts - Blast from the past: Sacrum