286 



OPEKATIONS ON BONES. 



Fig. 301.— Operation of Trephining. Modus Operandi. 



ary trephine (Fig. 300), and therefore not so safe. The single- 

 handed trephine is also to be preferred from the fact that the 

 former requires both hands to manage it, while the latter can be 

 manipulated with a single hand. They are both what might be 

 properly denominated true circular saws, if judged by the result 

 of their appUcation, which is the removal of a cii-cular portion of 

 the bony structiu'e, and a corresponding round ojDening, through 

 which other surgical indications can be fulfilled. 



A simple gimlet has often taken the place of the regular instru- 

 ment, but such an appliance can be considered as possessing little 

 more than the character of a mere exploring needle, from the 

 impossibility of making an opening with it of sufficient dimen- 

 sions to be available for any other practical use. 



