How the CricoThyroid muscle change phonation pitch
by National Center for Voice and Speech
This very brief (1 minute) video shows a demonstration of the action of the cricothyroid muscle in elongating and thinning the vocal folds, using an excised cow larynx.
Very helpful "3-D" view of anatomy, but the viewer should already be able to identify the cricothyroid muscle, or have a diagram nearby, before viewing.