TREPHINING OF THE FRONTAL SINUSES. 



23 



in^ on a level with the inferior border of the orbital cavity 

 on the lines FE, Plates V and VI. Trephining at this 

 point gives the operator access to the superior maxillary 

 sinus, SM, Plates IV-VI, through the fenestrum, FE, 

 Plates V and VI. The lowest and generally most essential 

 point for trephining is at ST, Plates IV and V, where the 

 opening affords free drainage externally from the most de- 

 pendent part of the cavity and at the same time offers 

 ample opportunity for securing dependent nasal drainage by 

 breaking through the superior turbinated bone at ST, 

 Plates IV, V and XI. 



By consulting Plates VII-IX, it will be seen that after 

 reaching the level of the nasal septum, a trephine opening 

 immediately against the median line like that at F, Plate 

 III would wound the septum and superior turbinated bone 

 and penetrate the nasal cavity. Consequently the operator 

 must avoid making the trephine opening in this region near 

 the median line, but must keep i^A to 2 inches laterally 

 therefrom. 



With a heavy convex scalpel make a circular incision at 

 the desired point 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 from the bone with the scalpel or 

 bone chisel. Control the hemorrhage. 



With the center-bit of the trephine extended place it accu- 

 rately upon the denuded area perpendicular to the surface 

 of the bone and grasping the handle firmly turn it to and 

 fro until the bit has penetrated the bony plate and the saw 

 has cut a distinct groove to serve as a guide when the center- 

 bit should be retracted and the operation continued until 

 the disc of bone is detached, being careful to maintain the 

 trephine perpendicular to the surface. The operation is 

 facilitated by grasping the shaft of the trephine between 



