Masseter muscle

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

It is particularly powerful in herbivores to assist when they are chewing plants.

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, the masseter is innervated by the mandibular division of the trigeminal nerve.