abnormal masticatory muscle morphology abnormal pterygoid muscle morphology MP:0004237 MPheno.ontology any structural anomaly of the muscles descending from the sphenoid bone to the lower jaw including the internal, or medial, pterygoid muscle and external, or lateral, pterygoid muscle; the action of the former is closing the jaws and that of the latter is opening the jaws, protruding the mandible, and moving the mandible from side to side