SURGICAL PUNCTURE, 



S7 



moreover the operator runs considerable risk of wounding himself. 

 The surgeon should possess sufficient delicacy of touch to know when 

 opposition ceases, that is when the cavity is entered. Supporting 

 the instrument with the ringers in the method described assists in 

 this respect. 



Other puncturing instruments are exploring needles and trocars. 



The trocar consists of a pointed steel rod provided with a metal 

 shield or tube, exactly corresponding with it in other respects but 

 a trifle shorter. The rod may be of varying length and thickness, 

 straight or curved, cylindrical or oval. The point is usually 

 triangular in section. At the lower end of the cannula, where it 

 abuts on the handle, are two holes or rings to permit of its being 

 fixed into position by tapes. As a rule the upper end of the cannula 

 discloses two short slits, which permit the parts to spring slightly 



Fig. 122. 



Fig. 120. 



Fig. 121. 



and apply themselves closely to a trifling circular depression formed 

 just behind the point of the trocar. This device causes the instru- 

 ment to enter much more easily, as the union of the trocar and the 

 cannula then presents no projection. The handle of the trocar is 

 grasped in the hollow of the hand, the fingers and thumb steady 

 the stem, and in use the instrument is thrust into the cavity to be 

 penetrated with a single rapid movement. The cannula is then 

 fixed with the left hand and the stilette or trocar removed with the 

 right. While withdrawing the cannula the trocar should be reinserted, 

 and the skin in the neighbourhood of the puncture should be pressed 

 down with the thumb and index finger of the left hand to prevent 

 it being lifted. 



Division of Hard Tissues. The horn of the hoof is divided with 

 a special knife grasped with the whole hand, Fig. 106. Bones are 

 divided with drills, chisels, saws, and forceps. The bone is prepared 



