The muscles of mastication (also known as masticatory muscles) are a group of muscles around the temporomandibular joint (TMJ) responsible for the movements at the mentioned joint, so they are also responsible for moving the lower jaw (mandible). 

Masticatory muscles participate in moving the mandible during eating and speaking. They assist while chewing and grinding the food. Therefore, the muscles of mastication also participate in opening and closing the mouth. These muscles elevate, depress, protrude, retract the mandible and provide side to side movements.

The masticatory muscles are divided into two groups - primary (main) and secondary (accessory) muscles of mastication. Each person has four pairs of primary muscles of mastication providing stability and movements at the TMJ and several accessory muscles participating in enabling jaw movements.

Primary muscles of mastication are:

• Temporalis
• Masseter
• Medial pterygoid
• Lateral pterygoid

Accessory muscles of mastication include:

• Buccinator
• Suprahyoid muscles (digastric, stylohyoid, mylohyoid, geniohyoid)
• Infrahyoid muscles (sternohyoid, sternothyroid, thyrohyoid, omohyoid)

Besides the classification described above, all these muscles can be divided into several more subdivisions depending on their function.

Muscles that elevate the mandible (close the mouth) are:

• Temporalis
• Masseter
• Medial pterygoid
• Lateral pterygoid (just its superior head)

Muscles that (along with gravity) participate in depressing the mandible (open the mouth) are:

• Lateral pterygoid (inferior head)
• Digastric (anterior belly)
• Mylohyoid
• Geniohyoid

Muscles that protrude the mandible include:

• Masseter
• Medial pterygoid
• Lateral pterygoid (inferior head)
• Digastric
• Temporalis

Muscles providing retrusion of the mandible are:

• Temporalis
• Digastric
• Lateral pterygoid (lower head)

Muscles providing side to side movements of the lower jaw include:

• Masseter
• Temporalis
• Medial pterygoid
• Lateral pterygoid