Tonsillar fossa

The tonsillar fossa (or tonsillar sinus) is a space delineated by the triangular fold (plica triangularis) of the palatoglossal and palatopharyngeal arches within the lateral wall of the oral cavity. In this space lie the palatine tonsils .

In many cases, however, this sinus is obliterated by its walls becoming adherent to the palatine tonsils.