Pl,ATE V. 



Trephining the Facial Sinuses. 



Cross section of tlie left side of the. head of an 

 aged horse at the second molar, seen from the 

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

 site the conmiunication between the nasal and 

 inferior maxillary sinuses ; IM, lateral portion 

 of inferior maxillary sinus ; IM', median portion 

 of inferior maxillary sintis ; SM, superior max- 

 illary sinus ; NF, superior maxillary division of 

 trifacial nerve in its bony conduit ; SZ, subz3'go- 

 niatic artery ; P, paUtine artery ; M2, second 

 molar. 



