Lateral pterygoid muscle

The lateral pterygoid (or external pterygoid) is a muscle of mastication with two heads.

Origin and insertion
The upper/superior head originates on the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone, and the lower/inferior head on the lateral surface of the lateral pterygoid plate.

Both heads insert onto the pterygoid fovea under the condyloid process of the mandible; the articular disc and fibrous capsule of the TMJ.

Innervation
The lateral pterygoid nerve - The mandibular branch of the fifth cranial nerve, the trigeminal nerve, innervates the lateral pterygoid muscle.

Function
It acts to lower the mandible, open the jaw, and help the medial pterygoids in moving the jaw from side to side (mastication).

Unlike the other three muscles of mastication, the lateral pterygoid is the only one that opens the jaw, or depresses the mandible. At the beginning of this action it is assisted by the digastric, mylohyoid and geniohyoid muscles.