[ 124 | 
fkull; afterwards, when the wings, fhoulders and ferule were 
laid afide, the faws were made of a pyramidal form, and were 
ferrated on the fides as well as at the edge. 
* Hester, fufficiently aware of the danger attending the 
trepan, advifes that when the fkull is fawed deep enough, which 
may be known by the circular piece being a little loofe, a terebra 
or gimlet fhould be fcrewed.into the hole made by the center- 
pin, and by the help of an elevator the piece is to be taken out ; 
if itis not loofe enough to come away, a few more turns of the 
faw are to be made, and the terebra applied again, to bring out 
the piece without hazarding the wounding the dura-mater by 
too frequent applications of the faw. And in all authors who 
have treated on this operation, we may find abundant cautions 
againft injuring the brain or its membranes, by a want of atten- 
tion, when the {kull was nearly perforated. Thefe confiderations, 
no doubt, determined + Mr. Chefelden, { Mr. Sharp, § Mr. Pott, 
and moft of the eminent Surgeons in England, to give the pre- 
ference to the trephine, as a more fafe and handy inftrument. 
The trephine has in refpeét of fafety fome advantage over the 
trepan ; the operator can with more readinefs apply it to any part 
of the head ; being fhorter, it is more manageable ; and as there 
is lefs occafion for preffure on it, there is confequently lefs hazard 
of 
* Heifter’s Surgery, part 2, chap. 41, page 361. 
+ Chefelden’s Obfervations on Le Dran’s Surgery, page 447. 
} Sharp’s Surgery, p..148. § Pott’s Works, Vol. I. p. 123. 
