plica semilunaris of the fauces plica semilunaris of the fauces the plica semilunaris is the thin upper part of the fold of mucous membrane in the supratonsillar fossa that reaches across between the two arches. a separate fold is called the plica triangularis which runs inferoposteriorly from the posterior surface of the palatoglossal arch to cover the inferior portion of the tonsil. plica semilunaris of the faucesdetailsidentifierslatinplica semilunaris fauciumta98a05.2.01.008ta22850fma55049anatomical terminology