Pl,ATE V. 



Trephining the Faciai, Sinuses. 



Cross section of the left side of the head of an 

 aged horse at the second molar, seen from the 

 front. F, frontal sinus ; N, nasal sinus, oppo- 

 site the communication between the nasal and 

 inferior maxillary sinuses ; IM, lateral portion 

 of inferior maxillary sinus ; IM', median portion 

 of inferior maxillary sinus ; SM, superior max- 

 illary sinus ; NF, superior maxillary division of 

 trifacial nerve in its bony conduit ; SZ. subzygo- 

 matic artery ; P, palatine artery ; M2, second 

 molar. 



