io6 



OPERATIVE TECHNIQUE. 



using the mallet or hammer. They have largely been replaced by 

 bone forceps, Fig. 132, which are made with blades either at right angles 

 to the long axis of the forceps or parallel with it. Each form has 

 special uses. 



Saws are of several forms. The frame saw (Fig. 133) consists of a 

 blade, a frame, and a handle. The blade is made somewhat finer 

 towards the back, so as to saw freeh' and not become fixed in the 

 furrow. It is secured at one end by a screw for regulating the tension, 

 and at the other carries a small rivet which prevents the blade slipping 

 through the slot into which it is introduced. The frame is either 

 quadrangular or semicircular. The handle was formerly provided 

 with depressions to fit the fingers. As, however, this rendered it 

 difficult to clean, modern saws are provided with plain curved handles. 



Fig. 134. — Chain saw. 



The nature of chain saws is almost sufficiently indicated b}' their 

 name. They consist of a number of articulated links, carr3'ing on one 

 side saw teeth (Fig. 134). On account of their cost, however, they are 

 not much used in veterinary surgery. The end of the chain is passed 

 around the bone by means of the needle and thread shown, and is then 

 attached to the handle ; by drawing the chain to and fro the bone is 

 graduall}' sawn through. A trephine consists of a hollo^^' steel 

 cylinder bearing teeth on its free border. A central terminal 

 steel point is usually added to steady the trephine in position, and by 

 rotating the handle alternately towards the right and left a circular 

 piece of bone is gradually cut through. Trephines are mostly used for 

 opening the sinuses of the face. 



