The masseter is a thick, strong muscle and typically the most prominent muscle of the jaw. It is located between the zygomatic arch and the mandible and has two parts. The larger, more superficial segment originates from a thick aponeurosis at the zygomatic process of the maxilla and the anterior two-thirds of the lower edge of the zygomatic arch. Dense fibers extend inferiorly and posteriorly then insert at the angle and lower half of the lateral surface of the mandible. The smaller, deeper segment originates at the posterior third of the lower border and entire medial surface of the zygomatic arch. This portion is more muscular in texture than its counterpart. The deep fibers extend inferiorly and anteriorly to insert at the upper half of the ramus and lateral surface of the coronoid process of the mandible.

The fibers of the two segments are continuous at the insertion, then diverge with the superficial portion angling forward and the deep portion back before inserting on the mandible. The overlap causes the superficial segment to obscure a portion of the deep segment. Additionally, the parotid gland, a large salivary gland, lies superficial and slightly posterior to the entire masseter muscle. Compared to other facial muscles, the masseter is relatively easy to locate and palpate, but these features must be considered when treating this area. (See “Take the Danger Out of Endangerment Sites” by Ruth Werner in the May/June 2020 issue of Massage & Bodywork, page 44, to read more about treating sensitive areas of the body.)

When activated, the two segments of the masseter oppose each other: the superficial portion pulls the mandible anteriorly, protracting it, whereas the deep portion pulls the mandible posteriorly, retracting it. These motions effectively cancel each other out, focusing effort into elevation of the mandible. The masseter is one of four muscles of mastication or chewing. For its size, it is extremely powerful and generates most of the force for biting and chewing. The medial and lateral pterygoid and temporalis muscles also contribute to this complex task.

The muscles of mastication, and particularly the masseter, can become hypertonic and painful in clients who clench their jaw, grind their teeth, or have other issues with the temporomandibular joint. There is also strong correlation between excessive tone in the masseter and upper neck tension and pain. Corresponding trigger points and ischemia may also cause headaches. Any or all of these may be initiated or perpetuated by chronic stress.

Masseter

Attachments

•
Origin: Zygomatic process of the maxilla and zygomatic arch of the temporal and zygoma bones

• Insertion: Angle, ramus, and lateral surface of the mandible

Actions

• Elevates the mandible

Innervation

• Mandibular division of the trigeminal nerve

Palpating Masseter

Positioning: client supine.

1. Sit at the client’s head, and locate the inferior edge of the zygomatic arch with your fingertips.

2. Slide your fingertips inferiorly toward the angle of the mandible and onto the fibers of the masseter. (Caution: Both the trigeminal nerve and the parotid gland are located in this region. To avoid them, carefully feel for the fibers of the masseter muscle when palpating.)

3. Follow the fibers of the masseter to its insertion on the inferior edge of the mandible.

4. The client gently opens and closes their mouth and/or clenches their jaw to ensure proper location.