TREPHINNIG OF THE FRONTAL SINUSES. 21 



3. TREPHINING OF THE FRONTAL SINUSES 



Uses. Fracture of the bony walls, necrosis, tumors. 



The ample communication below with the superior maxil- 

 ary sinuses prevents the accumulation of pus or fluids in the 

 frontal cavities even if formed therein unless the opening 

 between the superior maxilary sinus and the nasal fossa at N, 

 Plates V and VI becomes blocked, preventing the escape 

 of fluids through the latter and causing them to fill the 

 superior maxilary sinus and then back up into the frontal. 

 In case of empyema of the frontal sinus, trephining does not 

 give full relief but calls for a repetition of the operation on 

 the maxilary sinuses also. 



Instruments. Razor, scissors, convex scalpels, artery 

 forceps, tenacula, probe, trephine, curette, gouge, Luer's 

 sharp bone forceps, hammer, chisel, bone screw, lens-shaped 

 bone knife, probe-pointed bistoury, dressing forceps, disin- 

 fecting and dressing materials. 



Technic. Operate on the standing animal with the aid 

 of the twitch or secured in stocks, with local anaesthesia or 

 secure on the operating table or cast in lateral recumbency on 

 the sound side. Clip and shave the hair from the region of 

 the frontal bone on a level with the superior border of the 

 orbital cavity as indicated in Plate IV and disinfect the area 

 carefully. Within the shaved and disinfected area locate the 

 point for trephining, F, Plate IV, so that the inferior border 

 of the opening will be on a level with the superior border of 

 the orbital cavity at the dotted line below F and the inner 

 margin about i cm. from the median line of the face. With 

 a heavy convex scalpel make a circular incision as large as 

 the area of the trephine, directly through the skin, subcutem 

 and periosteum down to the bone and remove in one piece 

 the entire mass of encircled soft tissues by seizing the skin 

 with a tenaculum and forcibly separating the periosteum 



