[ 23g) 
Tae inftrument, which I have the honour of laying before this 
- Academy, Iam inclined to think will render that neceffary opera- 
tion of trepanning more eafy, more expeditious, and more fafe. 
If. I have fucceeded in this attempt, I thall efteem myfelf fortunate 
to have contributed to the improvement of fo ufeful an art as 
that of furgery ; but if I have done no more, I have offered ano- 
ther inftrument, to thofe already in ufe, for the operator to choofe 
from, in an operation which requires to be properly and cautiouily 
performed, and is frequently the chief, fometimes the on/y.relief 
for the perfon who has the misfortune.to be the fubje& of it: . In 
ufing this inftrument neither force nor preffure- is requifite; the 
left hand, which is employed to fuftain the inftrument, by being 
placed near the faw or crown; will keep-it fleady and firm to the 
place intended to be: perforated, while the right hand is engaged 
in turning the handle fafter or flower, as the operator fhall judge ex- 
pedient ; the points on w yhich the faw turns being at each end of 
the canula, and not refting on the two extremities of the inftru- 
ment (which is one of the faults of the trepan) will. require no 
more force or preffure on it, while working, than-what may be 
fufficient to keep’ the teeth of the faw in contact with the bone; 
confequently (preffure not being neceflary) all hazard of fuddenly 
_ entering or wounding the dura-mater or the brain is prevented. 
Tuts inftrument is compofed of a.crown or. faw made in the 
ufual form, and about an inch and an half from the crown is fixed 
_ to.a fpindle four inches and an half long, which is received into a 
barrel or canula of four inches in length; to the top of the fpindle, 
which is {quare above the canula, is applied a handle or winch, 
with a nut {crewed on the fpindle to keep the handle on; at the 
lower 
