Which muscle contributes to creating vertical lines in the forehead?

The corrugator supercilii is the muscle primarily responsible for creating vertical lines in the forehead. This muscle is located beneath the frontalis and originates from the superciliary arch of the frontal bone, inserting into the skin of the eyebrow. When the corrugator supercilii contracts, it pulls the skin of the forehead and eyebrows downward and inward, which leads to the formation of vertical furrows between the eyebrows, commonly referred to as "frown lines."

In contrast, the frontalis muscle is involved in elevating the eyebrows and creating horizontal wrinkles on the forehead when responding to expressions of surprise or questioning. The zygomaticus major is involved in smiling and elevating the corners of the mouth, which does not contribute to horizontal or vertical forehead lines. The orbicularis oris is responsible for controlling movements of the mouth and does not play a role in the formation of lines in the forehead area.

By understanding the specific functions of these muscles, one can accurately associate the corrugator supercilii with the creation of vertical forehead lines due to its unique action on the skin of the forehead and brow.