Plate III. 

 Trephining the Facial Sinuses. 



F, highest point at which an opening may be 

 made into the frontal sinus without wounding 

 the cranium and brain ; N, opening into nasal 

 sinus ; SM, opening into superior maxillary 

 sinus ; IM, opening into external portion of in- 

 ferior maxillary sinus ; IM', opening into the 

 median portion of the inferior maxillary sinus. 



