-5M 



FIG. 3. 

 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, open- 

 ing into external portion of inferior maxillary sinus ; IM', opening 

 into the median portion of the inferior maxillary sinus. 



