Isthmus of the fauces

The isthmus of the fauces or the oropharyngeal isthmus is a part of the oropharynx directly behind the mouth cavity, bounded superiorly by the soft palate, laterally by the palatoglossal arches, and inferiorly by the tongue.

The fauces are regarded as the two pillars, formed by the palatoglossus and the palatopharyngeus muscle, respectively, and covered with mucous membrane. The anterior one is known as the palatoglossal arch, and the posterior one is known as the palatopharyngeal arch. Between these two arches is the palatine tonsil.