In addition to defining the lower limit of the floor of the oral cavity, the free posterior border of the mylohyoid muscle on each side forms one of the three margins of a large triangular aperture (oropharyngeal triangle), which is a major route by which structures in the upper neck and infratemporal fossa of the head pass to and from structures in the floor of the oral cavity (Fig. 8.253). The other two muscles that complete the margins of the aperture are the superior and middle constrictor muscles of the pharynx.