Plate IV. 



Trephining the Faciai, Sinuses. 



F, opening into frontal sinus ; N, opening 

 into nasal sinus ; SM, opening into superior 

 maxillary sinvis ; IM, opening into external por- 

 tion of inferior maxillary sinus ; IM', opening 

 into the median portion of the inferior max- 

 illary sinus. 



