Pl,ATB III. 



TRapBiNiNG THE Factal 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. 



