This muscle lies on the side and front of the cranium, extending into the temporal fossa.

Origin. - From the outer surface of the parietal, squamous temporal, and frontal bones, in the temporal fossa, and from the sphenoid bone.

Insertion. - Into the coronoid process of the lower jaw and the anterior border of the same bone continuous with it.

Action. - To assist in masticating the food by bringing the lower jaw into contact with the upper and moving it from side to side.