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Portrait of Masseter

Anatomy · Muscles

Masseter

The muscle popularly called the strongest for its size

Head · muscle of mastication

A thick, four-sided muscle on the side of the face that runs from the cheekbone down to the angle of the lower jaw. It is the most obvious of the four chewing muscles and the one you can feel bulge under the cheek when you clench your teeth. It closes the jaw with great force.

How to spot them

  • ▸A thick quadrilateral muscle between the zygomatic arch above and the angle of the mandible below
  • ▸Feel it bulge in front of the ear and just above the angle of the jaw when the teeth are clenched
  • ▸The parotid duct crosses its surface, and the branches of the facial nerve run over it
  • ▸Supplied by a branch of the mandibular division of the trigeminal nerve, not the facial nerve

What to know

A thick chewing muscle from the zygomatic arch to the outer surface of the ramus and angle of the mandible

Masseter — the most superficial of the four muscles of mastication.

Often billed as the strongest muscle in the body for its size, thanks to its short, thick, multipennate fibres

Masseter — a popular claim with no agreed measure; anatomy texts say it is the most powerful of the chewing muscles.

Supplied by a nerve that comes off the anterior division of the mandibular nerve, V3 of the trigeminal, and passes through the mandibular notch

Masseter — the masseteric nerve; the facial nerve does not supply it, even though its branches lie across it.

The duct that carries saliva from the parotid gland passes across its outer surface before turning in through the cheek

Masseter — the parotid duct crosses it and then pierces buccinator.

Enlarges on both sides in people who grind their teeth, giving a square jaw; botulinum toxin is sometimes injected to slim it

Masseter — masseteric hypertrophy in bruxism.

Superficial and deep parts fuse at the lower end, and it closes the mouth by raising the lower jaw

Masseter — elevation of the mandible; the superficial part also helps to protrude it.

Its spasm in tetanus fixes the jaw shut, the sign known as lockjaw

Masseter — trismus; it is also the muscle tested in the jaw-jerk reflex, which depends on V3.

Key ideas

  • It is short and thick and acts close to the tooth row, so the force it delivers is greatest on the molar teeth; the fan-shaped temporalis assists in closing the jaw and its rear fibres pull the jaw back.
  • Its fibres run down and slightly back, so the superficial part also draws the jaw forward as it closes it, while the deep, near-vertical fibres pull it straight up and back.

Quick-fire facts

  • •One of the four muscles of mastication (masseter, temporalis, medial pterygoid and lateral pterygoid), all supplied by the mandibular nerve, V3
  • •Origin: the zygomatic arch and the maxillary process of the zygomatic bone (superficial part from the front two-thirds, deep part from the back third and inner surface)
  • •Insertion: lateral surface of the ramus and the angle of the mandible
  • •Action: elevates the mandible to close the mouth; the superficial part helps to protrude it
  • •Nerve supply: masseteric nerve from the anterior division of the mandibular nerve (V3)
  • •Blood supply: masseteric artery, a branch of the maxillary artery, plus the transverse facial artery
  • •The parotid duct runs across it about a finger's breadth below the zygomatic arch, and it can be felt with the mouth open
  • •Standard sources call it the most powerful of the muscles of mastication; the wider popular claim that it is the strongest muscle in the body, weight for weight, has no agreed measure behind it (other muscles, such as the soleus or gluteus maximus, win on other measures)
  • •Named from the Greek masetér, a chewer
  • •Bruxism (clenching and grinding of the teeth) can enlarge it and produce pain in front of the ear

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Sources