As mentioned before, there are four paired primary muscles of mastication:

All these muscles elevate the mandible (close the mouth) except for the lateral pterygoid, which depresses (opens the mouth) and protrudes it (moves it forward). All primary muscles of mastication:

Act at the temporomandibular joint by moving the lower jaw;
Originate from the skull and insert on the mandible;
Are innervated by branches of the mandibular nerve (CN V3);
Receive their blood supply from the maxillary artery.

Another shared feature of the masticatory muscles is that they insert on the posterior half of the mandible. The mandibular ramus, angle, neck and coronoid process are extensively clothed in muscle insertions.

Overall, each muscle acts in all dimensions to:

Elevate or depress the mandible (open or close the mouth)
Protrude or retract it (move the mandible forward or pull it backward)
Rotate the mandible (provide side-to-side movements)

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Primary muscles of mastication