In human anatomy, the masseter is one of the muscles of mastication.

In the animal kingdom, it is particularly powerful in herbivores to facilitate chewing of plant matter.

It is the muscle which causes the jaws to bite, and is the most powerful muscle of the human body, with a record bite of 990 pounds observed in a man who suffered an epileptic seizure, which caused him to bite uncontrollably. This shattered most of his teeth. Were the teeth of a human able to withstand the sufficient pressure, a human could bite a hole into an automobile tire inflated to 65 psi, chew up a cinder block, or bite through the rings or chain of a pair of handcuffs.

Origin and insertion of the two heads

The masseter is a thick, somewhat quadrilateral muscle, consisting of two portions, superficial and deep.

The fibers of the two portions are continuous at their insertion. The masseter muscle is sometimes the target of plastic jaw reduction surgery.

Superficial

The superficial portion, the larger, arises by a thick, tendinous aponeurosis from the zygomatic process of the maxilla, and from the anterior two-thirds of the lower border of the zygomatic arch.

Its fibers pass downward and backward, to be inserted into the angle and lower half of the lateral surface of the ramus of the mandible.

Deep

The deep portion is much smaller, and more muscular in texture.

It arises from the posterior third of the lower border and from the whole of the medial surface of the zygomatic arch

Its fibers pass downward and forward, to be inserted into the upper half of the ramus and the lateral surface of the coronoid process of the mandible.

The deep portion of the muscle is partly concealed, in front, by the superficial portion; behind, it is covered by the parotid gland.

Innervation

Along with the other three muscles of mastication (temporalis, medial pterygoid and lateral pterygoid), the masseter is innervated by the mandibular division of the trigeminal nerve.

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