New Injlrumeni for Trepanning. 20q 



points of the circle alike, one or other of the legs may be 

 lengthened or {hortened at pleafure, by means of the fetting 

 fcrexvs ; and in this manner ii may be made to fit exaftly. 



The next ftep of the operation is, to cut the pericranium 

 with one or two turns of the inftrument, and, if neceflary, 

 that portion of the membrane within the circle of the faw 

 may be removed with the fingers. The fawing is now begun 

 by turning the handle with one hand, and holding the in- 

 ftrument °firnily with the other. Thus the bone may be 

 cut very quickly ; and if the furgeon wifli to proceed cau- 

 tioufly towards'the end of the operation, he may then work 

 the inftrument in the manner of the trephine, which can be 

 done bv grafping the handle with one hand, and fupporting 

 the frame as before mentioned. 



The fimplicity of the inftrument, and the mode of ope- 

 ratino- with it, Will be better underftood by the following 

 defcriptlon : 



A, A, the handle, (Plate VII ;) B, B, the axle, pafling 

 through D, the upper part of the frame; and C, the croi^:- 

 band.° E,E,E, the fides of the frame; F,F,F, the feet or 

 refts, which (lide in the fides of the frame K,K,K, and are 

 faftened with thumb-fcrews b,b; G, the cutting-head, fixed 

 on the end of the axle; H, a collar which Aides upon the 

 axle, and can be made taft upon it with the thumb -fcrew a. 



The fliding-coUar may be ufed with advantage when the 

 furceon is afnild of plunging the head of the inftrument into 

 the^brain during the operation ; for, by fixing it at a certain 

 diftance above the crols-band, it will reft upon it, fooner or 

 later, according to the intention of the operator, and prevent 

 the inftrument from pafling deeper until the collar be ftiiftcd. 

 For this reafon, as well as the fuperiority of the inftrument 

 in general to thofe in common ufe, it is particularly recom- 

 mended to furgcons who may have fre(]ucnt occafion to per- 

 form this operation on board a fliip &t feu. 



VoL.vr. Kft IV. 0^. 



