316 



TREPHINING INSTRUMENTS. 



made with an ordinary borer (exfoliative trephine, Fig. 314), but 

 if it is merely necessary to make an aperture in the bone, the per- 

 forating trephine is used (Fig. 315). The last-named instruments 

 can, however, generally be dispensed with. 



The superior maxillary sinus in the horse is generally divided by 

 a thin plate of bone into an upper larger and a lower smaller division. 

 Lanzilotti describes this plate as having been present in 52 out of 

 74 cases operated on. It lies nearly in the centre of a rectangle, 



Fig. 308.— Stock trephine. Fig. 309.— Hand trephine 



whose longer sides are formed by the zygomatic ridge, and a line 

 drawn parallel with it starting from the inner angle of the eye, and 

 whose shorter side's are bounded by the rim of the orbit and a line 

 drawn perpendicularly to the lower end of the zygomatic process 

 of the malar bone (see Figs. 316 and 317). According to Lanzilotti, 

 the septum is always wanting in the ass, and often in the mule. 

 Trephining about 1£ inches above the lower end of the zygomatic 

 ridge, and f to 1J inches away from it, this division is cut into, and 

 both portions of the sinus are opened. Where one sinus alone has 

 been opened, the dividing wall can be broken down. In young 



