TRTCrTTlNTNf! THE FRONTAL STNTTS. 



319 



In opening the frontal sinus the bone is trephined at a point 

 midway between the internal angle of the eye and the middle line 

 of the frontal region. Here the skin lies almost immediately on the 

 periosteum. A V-shaped incision, with the angle directed down- 

 wards, is made through the skin and periosteum, the flap of skin 

 is turned upwards, and the periosteum is removed to an extent equal 

 to the diameter of the trephine crown. With the gimlet an opening 

 is made in the centre of the uncovered bone, then the trephine is 



Fig. 317. — Lateral view of horse's skull ; the facial sinuses exposed. 

 a, Posterior portion of frontal sinus ; a ', anterior portion of same ; a", the septum 

 dividing them ; b, posterior portion of the anterior turbinated bone ; c, cavity 

 of nostril ; d, ethmoid bone ; e, superior maxillary sinus (lower part), which 

 is" divided from the upper part hh by the thin septum i ; e bony plate forming 

 the lateral boundary of the posterior turbinated bone / ; g, infraorbital canal ; 

 k, line dividing the upper (thin) from the lower (thick) portion of the septum ; 

 m, lower margin of the maxillary sinus ; n, nasal duct ; o, orbit ; p, zygomatic 

 ridge. 



applied, and the operation completed as described under trephining 

 the superior maxillary sinus. 



The opening should not be made too near the cranial cavity. 

 A line connecting the right and left supra orbital foramina indicates 

 the upper limit of the operation field. If the opening is made too 

 high the trephine may damage the lateral mass of the ethmoid bone ; 

 besides there is no disadvantage in entering the frontal sinus at a 

 lower point. 



During the first three or four days after operation the artificial 

 openings may remain blocked with blood or pus, but at the end of 

 that time discharge occurs freely and recovery is usually easy. 



After-treatment must depend on the nature of the disease. In 

 chronic catarrh, flushings of the affected sinus with antiseptics like 

 boracic acid, hydrogen peroxide, iodine, and carbolic acid, are 



