Masseter muscle

Origin and insertion 

The superficial part of the muscle that lies over its deep part originates from the maxillary process of the zygomatic bone. It then runs inferoposteriorly to the masseteric tuberosity found on the lower part of the superficial side of the ramus of the mandible.

The deep part consists of vertically directed muscle fibers. This part originates from the entire length of the inferior border of the zygomatic arch, and inserts onto the superficial side of the ramus of mandible, superior to the insertion of the superficial part of the muscle.

With this position, the muscle can be easily palpated from the oral cavity along the cheek. Furthermore, some of the deep fibers radiate into the anterior capsule and articular disc of the temporomandibular joint.

Need to learn the origins and insertions (plus innervations and functions!) of the masseter muscle as quickly as possible? Our head and neck muscle anatomy chart will cut your time in half. 

Relations 

The entire superficial (lateral) aspect of the muscle is covered with thin but very strong masseteric fascia. 

Also on the superficial side, below the zygomatic process, the duct of the parotid gland passes across the surface of the muscle. This duct courses mostly over the anterior part of the lateral aspect, i.e. it is located anterolaterally. 

The superficial part of the gland itself is also located superficially to the masseter, but a bit more posteriorly, i.e. posterolaterally to the muscle.

Along with the parotid gland, a few more structures can be found over the lateral side of the muscle:

• Terminal branches of the facial nerve
• Facial vein
• Facial artery
• Risorius muscle
• Zygomaticus major muscle

The medial, or inner, surface of the muscle is mostly related ramus of mandible almost completely covering its superficial surface.

The medial aspect of the masseter muscle forms the lateral wall of the facial space called the submasseteric space. It is a paired potential space between the lateral aspect of the mandible and medial aspect of the masseter muscle.
Located deep to the posterior part of the inner aspect of the muscle, or simply posteromedially, the temporal muscle is found.

Anterior to the muscle, the buccinator muscle is located. The abovementioned duct of the parotid gland actually penetrates the fibers of the buccinator muscle to find its way to the inside of the oral cavity and finally open onto the inner side of the cheek.

The posterior aspect of the muscle is located anteriorly to the deep part of the parotid gland. This practically means that the parotid gland surrounds the entire posterior and most of the superficial aspect of the muscle.

Innervation

Like all the muscles from the masticatory group, the masseter muscle is innervated by the special branch of the mandibular nerve, called the masseteric nerve.

Blood supply

The masseter muscle is supplied with blood by the masseteric artery, a branch of the maxillary artery. 

Function 

The masseter is one of the four muscles of the masticatory apparatus. It elevates the mandible causing a powerful jaw closure. The contraction of the superior part, which runs diagonally to the front, moves the mandible forward (protrusion). Furthermore, the muscle helps stabilize tension of the articular capsule of the temporomandibular joint.

Do you want to learn more about the masseter muscle and other masticatory muscles? Then take a look at the following quiz!