Muscles of the head and neck

The mandible is the lower jaw, the only movable bone of the skull. The maxilla forms the upper jaw, and the zygomatic bone is the cheekbone.

• Maxilla:
• Correct: Mandible:
• Zygomatic bone:

The hyoid hangs in the neck from muscles and ligaments and forms no joint with any other bone.

• It forms a joint with the mandible:
• Correct: It forms no joint with any other bone:
• It is part of the cervical vertebrae:

Muscle names often list the attachments, origin first. The sternohyoid runs from the sternum to the hyoid bone.

• Its shape:
• Correct: Its attachments: from the sternum to the hyoid:
• Its number of heads:

The ring of muscle around the eye is the orbicularis oculi. It closes the eyelids.

• Orbicularis oris: The orbicularis oris is the ring around the mouth, not the eye.
• Correct: Orbicularis oculi: Correct. The ring around the eye is the orbicularis oculi.
• Occipitofrontalis, frontal belly: The frontal belly of the occipitofrontalis lies over the forehead, above the eye; it raises the eyebrows rather than closing the eye.
• Temporalis: The temporalis is a chewing muscle on the side of the skull, under the scalp, not around the eye.

The masseter runs from the zygomatic arch down to the outer surface of the angle of the mandible. It is the prime mover of jaw closing.

• Temporalis: The temporalis fans over the side of the skull above the ear, not over the angle of the jaw.
• Buccinator: The buccinator lies forward in the cheek wall and moves the cheek, not the jaw.
• Medial pterygoid: The medial pterygoid inserts on the inner surface of the angle of the mandible, hidden from this outside view.
• Correct: Masseter: Correct. The thick muscle over the angle of the jaw is the masseter.

The sternocleidomastoid runs from the manubrium and medial clavicle up and back to the mastoid process behind the ear.

• Anterior and middle scalenes: The scalenes lie deeper and lower on the side of the neck, running from the cervical vertebrae to the first two ribs.
• Omohyoid: The omohyoid is a thin infrahyoid strap muscle running from the scapula to the hyoid.
• Correct: Sternocleidomastoid: Correct. The long diagonal muscle from sternum and clavicle to the mastoid process is the sternocleidomastoid.
• Digastric: The digastric is a suprahyoid muscle under the jaw.

The orbicularis oculi closes the eyelids, so its weakness leaves the eye partly open. The buccinator presses the cheek against the teeth and pushes food back onto them, so its weakness lets food collect in the cheek.

• Masseter and temporalis: The masseter and temporalis close the jaw. Weakness would make biting weak, not keep the eye open or let food pocket in the cheek.
• Frontalis and zygomaticus major: The frontalis raises the eyebrow and the zygomaticus major lifts the corner of the mouth. Neither closes the eye or clears the cheek.
• Correct: Orbicularis oculi and buccinator: Correct. The eye sphincter and the cheek muscle explain both problems.
• Medial and lateral pterygoid muscles: The pterygoids move the jaw forward and side to side. They do not close the eye or press the cheek to the teeth.

The muscle pulls the mastoid process toward the sternum and clavicle on the same side. That tilts the head toward the right shoulder and, because the mastoid is behind the ear, swings the face toward the left.

• Correct: It tilts toward the right shoulder and the face turns to the left: Correct. Same-side tilt, opposite-side turn.
• It tilts toward the left shoulder and the face turns to the right: This describes the left sternocleidomastoid.
• The chin drops straight down to the chest: Straight neck flexion needs both sternocleidomastoids contracting together.
• The head tips straight back: Tipping the head back is extension, done mainly by muscles at the back of the neck.

The masseter, temporalis and medial pterygoid all insert on the mandible and pull it up. The lateral pterygoid and the suprahyoid muscles, such as the digastric, help open the jaw instead.

• Correct: Masseter: Yes. The masseter is the prime mover of jaw closing.
• Correct: Temporalis: Yes. The temporalis elevates and retracts the mandible.
• Correct: Medial pterygoid: Yes. The medial pterygoid elevates the mandible from the inside, mirroring the masseter.
• Buccinator: No. The buccinator is a muscle of facial expression: it presses the cheek to the teeth but does not move the jaw.
• Digastric: No. The digastric is a suprahyoid muscle; with the hyoid held still it pulls the mandible down, opening the mouth.

The suprahyoid muscles run from the hyoid up to the mandible and skull, so they pull it up. The infrahyoid muscles run from the hyoid down to the sternum, voice box and scapula, so they pull it back down.

• Infrahyoid muscles raise them; suprahyoid muscles lower them: This reverses them. Muscles below the hyoid pull it down, not up.
• Correct: Suprahyoid muscles raise them; infrahyoid muscles lower them: Correct. Above pulls up, below pulls down.
• Scalenes raise them; sternocleidomastoids lower them: The scalenes attach to the vertebrae and ribs, and the sternocleidomastoids to the sternum, clavicle and mastoid. Neither attaches to the hyoid.
• Masseters raise them; gravity alone lowers them: The masseters attach the zygomatic arch to the mandible and never reach the hyoid; muscles below the hyoid actively pull it down.