140 ELEMENTARY OPERATIONS. 



handle rests on the back of the hand, with the fingers shghtly 

 flexed. The joint, brought close to the skin, and perpendicular to 

 it, is thrust by the extension of the fingers through the tegument 

 and tissues underneath and then drawn out perpendicularly, un- 

 less it is desu^able to increase the size of the incision, when the 

 division is made by extending the incision from within outward. 

 Puncture withthe Straight Bistoury. — The bistoury, for this 

 purpose, must be finely pointed and sharp. Held as a writing pen, 

 with its edge upward or downward, or as a table-knife, accord- 

 ing to the thickness of the tissues, and its action hmited by ha\^ng 

 the fingers at a given distance from the point, it is pushed per- 

 pendicularly and more or less rapidly at once to the necessary' 

 depth. It is then drawn out, unless the incision is to be 

 enlarged, which is done by a motion from within outward 

 by the blade. Sometimes the instrument is pushed into the 

 tissues in an obhque, instead of a perpendicular dii-ection, when it 

 is not desirable to have communication between the ojDening of 

 the skin and the one directly beneath it. This constitutes the first 

 step of the subcutaneous incision. 



Fig. 175.— Trocar and Canula. 



Puncture loith the Trocar. — This instrument is composed 

 of two parts. A rod, secm-ed to a firm handle at one extremity 

 and terminating at the other in a tri-f aced point, is one ; this rod 

 fits into a canula, blunt at one end and ha\dng at the other a cuj)- 

 shaped flange, which is the other part. The canula is long enough 

 to receive the entire length of the rod, except the tri-faced j^oint, 

 which projects beyond it. The two parts are fitted closely 

 together. 



■ Trocars are of various size and form, being both straight and 

 ciun^ed. That which is used for hyovertebrotomy is the longest of 

 all ; those used for rumenotomy are quite large in diameter ; the 

 enterotome is, on the contrary, quite small. 



