The anterior portion of the trachea (windpipe) of tetrapod vertebrates, which in amphibians, reptiles, and mammals contains the vocal cords. Movement of the cartilage in the walls of the larynx (by means of the laryngeal muscles) alters the tension of the vocal cords. This changes the pitch of the sound emitted by the vocal cords when they vibrate. The final voiced sound is modified by resonance within the oral and nasal cavities.