pterygoid muscle morphology trait pterygoid muscle size trait VT:0004238 Trait.ontology Any measurable or observable characteristic related to the physical magnitude of either or both 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; 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. masticatory muscle size trait