Masseter

Musculus masseter

Also known as: chewing muscle

A thick quadrilateral muscle from the zygomatic arch to the angle of the mandible. It is the most powerful elevator of the jaw and one of the strongest muscles for its size.

Show on body map

Overview

Masseter has a superficial part, running from the zygomatic process of the maxilla and the anterior two-thirds of the zygomatic arch down and back to the angle and lower lateral ramus, and a deep part, running from the posterior third and medial surface of the arch to the upper ramus and coronoid process. With the medial pterygoid on the inside of the ramus, it forms a pterygomasseteric sling that suspends the angle of the mandible and generates a very large bite force.

It is easily felt over the angle of the jaw when the teeth are clenched. The parotid duct runs across its surface a finger-breadth below the zygomatic arch before turning medially to pierce buccinator, and branches of CN VII fan out over it. Its nerve, the masseteric nerve (V3), reaches it through the mandibular notch.

Location: Lateral surface of the ramus of the mandible.

Parts & subdivisions

Superficial part
Larger. Its fibres run downward and backward and contribute to protrusion.
Deep part
Its fibres run vertically. It helps retract the mandible.

Anatomy

Origin: Superficial part: zygomatic process of the maxilla and the anterior two-thirds of the inferior border of the zygomatic arch. Deep part: posterior third and medial surface of the zygomatic arch.
Insertion: Angle and lateral surface of the ramus of the mandible, up to the coronoid process.
Action: Elevates the mandible (closes the jaw). Superficial part assists protrusion; deep part assists retraction.
Innervation: Masseteric nerve (anterior division of the mandibular nerve, CN V3).
Nerve roots: Cranial nerve V3 (trigeminal motor nucleus, pons); no spinal roots
Arterial supply: Masseteric artery (maxillary artery), transverse facial artery (superficial temporal artery) and the facial artery.
Relations: Crossed by the parotid duct, the transverse facial artery and branches of the facial nerve. The parotid gland overlaps its posterior border.

Function

Elevates the mandible (biting, chewing)
Superficial fibres assist protrusion; deep fibres assist retraction

Clinical significance

Trismus

Spasm of masseter limits mouth opening ("lockjaw"). Causes include dental abscess, peritonsillar abscess, tetanus and radiotherapy.

Masseteric hypertrophy

Bruxism or habitual clenching can enlarge masseter, giving a square jaw. Botulinum toxin injection reduces it.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.