Muscular Anatomy of the Face
There are quite a few anatomy resources on the web, but not a lot that combine clear illustrations with pictures of the muscles in action.
With the help of a patient model and a fine illustrator, I hope this resource helps clarify how the face can make so many expressions.
You will also find a link to my Craniometric Landmarks web app which is a part of my online forensic sculpture class.
It's called the mentalis because it emanates from the mental eminence on the mandible. This muscle flattens the chin and pushes the middle of the lower lip upwards, and the outer edges downwards. The chin becomes dimpled when this muscle acts. Cleft chins are a result of a cleft in the mandible, not the action or formation of this muscle. The young man in the images is also contracting his buccinator, leading to the dimples at the corner of his mouth as well.
The Nasalis muscle originates on the side of the nose near the middle of the nose's length, this strip like muscle inserts into muscles along the side of the nose and also the wing of the nose. When we wrinkle our nose, we are using this muscle to pull our nostril upwards, thereby compressing and deforming the skin above it. The model is also contracting the Levator labii muscles, his corrugator and procerus, among others to make these expressions.
This circular flat muscle surrounds the eye and eyesocket. The muscle has a great expressive capacity, as it can act in part, or all together to help us squint or simply smile with the corners of our eye. The young man is smiling naturally, and the lower half of the Orbicularis oris contracts to give his eyes a feeling of laughter.
The Orbicularis oris is a circular muscle that surrounds the lips. The muscle can act in part or all together to create a vast number of expressions. Additionally, many muscles meet along its edges, which further varies its influence on expression. In the images, below, the muscle is contracted so that the lips are pushed forward into a pucker.
The Procerus is a small muscle that originates at the bridge of the nose that inserts in the skin between our eyebrows. It leads to the vertical wrinkles between the eyes seen when people express anger. The young man in the pictures is using several muscles in addition to the procerus in his expression including the Orbicularis occuli, Levator labii muscles, the Nasalis, and the Corrugators.
The Risorius is a thin muscle that draws the corners of the mouth back and outwards. It extends from the Masseter to the outer edge of the Orbicularis oris. It contributes to the widening of the mouth with a smile. In the first image of the young man, you can see he's also smiling nicely with his eyes by contracting the lateral margins of the Orbicularis occuli.
This muscle originates in the temporal region of the calvarium and converges in a rope-like insertion on the coronoid process of the mandible. We use this muscle to close our jaw.
The Zygomaticus (some anatomists divide it into major and minor components) originates on our zygomatic arch and inserts into the outer margin of the Orbicularis oris. The muscle draws the corner of our lips back, laterally, and to a lesser degree upwards. We use this muscle when we smile. When contracted, it compresses the cheek tissue along its length and can give people apple cheeks when they smile.