Superficial part of masseter

At a glance

English

Superficial part of masseter

Latin (TA2)

Pars superficialis masseteris

System

Muscle

Region

Head

Side

Paired, left and right

About the superficial part of masseter

The masseter is the strongest and most easily felt of the muscles of mastication: clench the teeth and it hardens into a thick pad over the back of the cheek. It is a thick, roughly four-sided muscle made of two layers that join at their lower ends. The superficial part is the larger and covers most of the deep part; it lies just under the skin, the parotid gland and duct, and branches of the facial nerve.

It springs by a strong tendinous aponeurosis from the zygomatic process of the maxilla and from the front two thirds of the lower edge of the zygomatic arch. Its fibres slope downwards and backwards, and end on the mandibular angle and on the outer face of the lower ramus. Because its fibres slope backwards as they descend, the superficial layer differs in direction from the more upright deep layer, and at the lower border it meets the medial pterygoid tendon to form a sling under the angle of the jaw.

Acting on both sides, the masseter raises the mandible and closes the mouth with great force, working with the temporalis and the medial pterygoid; it is the main power of the bite between the back teeth. The forward slope of the superficial fibres also lets them help push the lower jaw forwards, and one side can assist small side-to-side movements in grinding. Like the other chewing muscles it is supplied by the masseteric nerve from the mandibular division of the trigeminal nerve, and it receives blood from the masseteric branch of the maxillary artery and from the facial and transverse facial arteries.

To examine it, the doctor or dentist places a hand over each cheek and asks the patient to clench several times, feeling for equal hardening. Habitual clenching, grinding or constant gum chewing can thicken the muscle, a painless swelling known as masseteric hypertrophy that may be one-sided or uneven and can be mistaken for parotid disease, a dental abscess or a tumour. Its outline, which follows the muscle exactly, is the clue. Spasm of the masseter is also an early warning sign of malignant hyperthermia during anaesthesia.

Attachments, action and supply

Origin

Zygomatic process of the maxilla and the front two thirds of the lower border of the zygomatic arch, by a thick aponeurosis.

Insertion

Angle of the mandible and the outer face of the lower half of the ramus.

Action

Elevates the mandible to close the jaw powerfully; helps protrude it.

Nerve supply

Masseteric nerve, a branch of the mandibular nerve (V3).

Blood supply

Masseteric artery from the maxillary artery, with branches of the facial and transverse facial arteries.