Mouthpiece

n.
  1. The part of a musical or other instrument to which the mouth is applied in using it; as, the mouthpiece of a bugle, or of a tobacco pipe.
  2. An appendage to an inlet or outlet opening of a pipe or vessel, to direct or facilitate the inflow or outflow of a fluid.
  3. One who delivers the opinion of others or of another; a spokesman; as, the mouthpiece of his party.

This is a term that was used sometimes in old movies. When a tough bad guy was arrested he might say “I ain't sayin' nothin' without my mouthpiece!”