The corrugator supercilii

is a
small, narrow
pyramidal muscle

located at
the medial end
of the eyebrow.

Its fibers
pass upward
and laterally.

as the principal
muscle of suffering

the muscle is
sometimes severed
or paralyzed with

botulinium toxin
as treatment for migraine
or for aesthetic reasons.

From the Wikipedia entry for Corrugator supercilii muscle. Submitted by Dawn Corrigan.