Final answer:
The corrugator supercilii is a facial muscle responsible for frowning and creating vertical forehead wrinkles by drawing the eyebrows down and together.
Step-by-step explanation:
The corrugator supercilii muscle is a small, narrow muscle located at the inner end of the eyebrow, beneath the frontalis and just above the eye. Its primary function is to draw the eyebrows downward and medially, causing the vertical wrinkles on the forehead, which often are associated with frowning. The action of the corrugator supercilii contributes to facial expressions that convey emotions such as worry, concentration, or anger. Together with other muscles, such as the buccinator muscle which compresses the cheek allowing actions such as whistling and sucking, the corrugator plays a significant role in the muscles of facial expression. These muscles insert into the skin and move the skin rather than bones to create facial expressions.