TREPHINING THE FACIAL SINUSES. 315 



After trephining, the contents of the sinuses are washed out by 

 injecting a disinfecting solution, such as boracic acid, potassium 

 permanganate, hydrogen peroxide, or iodine, and closure of the 

 openings is prevented by inserting plugs of tow or jute, or corks. 

 Irrigation must be repeated daily, until the nasal discharge ceases. 



(E) TREPHINING THE SUPERIOR MAXILLARY AND FRONTAL 



SINUSES. 



Trephining is resorted to in the treatment of empyema of the 

 facial sinuses, necrosis of the turbinated bones, in removing tumours 

 or foreign bodies from the nasal chambers or sinuses, and in punching 

 out certain molar teeth. 



Various instruments are used for removing portions of bone from 

 the walls of the skull. 



(1) The trephine, a circular-shaped saw, which is either affixed 

 to a stock similar to a carpenter's (stock trephine, Fig. 308), or to a 

 handle (hand trephine, Fig. 309). Usually the latter simple form 

 is used. The crown, a steel cylinder of varying size, which forms 

 the saw, is smooth on its external surface, differing in this respect 

 from those formerly in use (trepans), which were conical, and provided 

 externally with sharp saw teeth to allow of their entering the bone. 

 In the centre of the crown stands the centre pin, a piece of steel which 

 can be fixed by means of a screw, and caused to project somewhat 

 beyond the cutting edge of the crown. 



(2) A small gimlet to perforate the bone for the centre-pin of the 

 trephine. 



(3) The bone screw (Fig. 310) carries at one end a ring, by which 

 it is held. The other end is fashioned into a conical screw, which 

 can be used as a perforator, or to remove the disc of loose bone : 

 under certain circumstances the screw may be used to bring depressed 

 bone into its former position, but for this purpose the elevator 

 (Fig. 310a) may be found more convenient. *c. 



(4) The lenticular knife (Fig. 312). With this the sharp edges 

 of the opening left by the trephine are removed, to prevent the finger 

 being injured when introduced during examination. 



(5) The " periosteum knife " (Fig. 313) is for scraping the 

 periosteum from the point of operation, but may be replaced by a 

 blunt knife, curette or gouge. The set of instruments usually 

 comprises a chisel (Fig. 311) and saw to remove pieces of bone such as 

 those between two trephine apertures, and is useful in making large 

 openings. Where a trephine is not to hand, the opening may be 



