Masseter

The masseter is one of the four primary muscles of mastication. It is a thick, quadrilateral, and powerful muscle located in the lateral aspect of the face, covering the ramus of the mandible. Its main function is to elevate (close) the mandible, playing a key role in chewing and clenching the teeth.

Anatomical details

1. Origin

• Superficial part: From the maxillary process of the zygomatic bone and anterior two-thirds of the zygomatic arch.

• Deep part: From the posterior third of the zygomatic arch and its medial surface.

2. Insertion

From their origin, the masseter muscle fibres run downward and slightly backward:

• Superficial fibres: Insert into the angle and lower lateral surface of the ramus of the mandible.

• Deep fibres: Insert into the outer surface of the upper part of the ramus and the coronoid process of the mandible.

Innervation

• Masseteric branch of the mandibular nerve (CN V₃) — a motor branch that passes through the mandibular notch to reach the muscle.

Blood Supply

• Masseteric branch of the maxillary artery

• Also receives contributions from the facial artery and transverse facial arterial branch of the external carotid artery.

Actions

• Elevation of the mandible — closes the mouth (main action).

• Protrusion (superficial fibres): Assists in pushing the mandible forward. Damage to CN V3 leads to weakness or paralysis → deviation of mandible toward affected side on opening.