PI.ATE VI. 

 TREPHINING THE FACIAL SINUSES. 



Cross srction, slightly oblique, through left 

 half of head at fiist molar in a two year colt. 

 F, frontal sinus ; N, nasal sinus at point of com- 

 munication with the inferior maxillary sinus, 

 IM ; IM', median portion of inferior maxillary 

 sinus; SM, superior maxillary sinus ; Mi, first 

 molar ; M2, second molar ; P, palatine artery ; 

 SZ, sub-zygomatic arttry. 



