Plate IV. 



Trephining of Faciai, Sinuses. 



Cross section of the right half of the head of 

 a horse at the posterior border of the last molar. 

 F, frontal sinus ; IM, lateral portion of inferior 

 maxillary sinus at extreme posterior or superior 

 part ; IM', median portion do. ; N, nasal 

 chamber opposite the communication between 

 it and the superior maxillary sinus ; NF, con- 

 duit of superior maxillary branch of the trifacial 

 nerve ; S M, superior maxillary sinus ; M', 

 fragment of last molar. 



