Plate IX. 



Trephining the Facial Sinuses. 



Cross section obliquely downwards and back- 

 wards through the right half of the head of a 

 two-year old colt at the first molar. F, frontal 

 sinus ; N, nasal passage at point of communica- 

 tion with the inferior maxillary sinus, IM ; IM^, 

 median portion of inferior maxillary sinus ; SM, 

 extreme lower end of superior maxillary sinus 

 opened; Mi, first molar; M2, second molar; 

 P, palatine artery ; SZ, sub-zygomatic artery. 



