SURGERY. 209 



the shaft of the perforator, which is held in place by the small spring, o, 

 worked by an external lever, p. 



Bichat's trepan^ fig. 63, consists of a handle part, 5, surmounted by a head, 

 a, and to whose lower end, instead of a tube, is attached a hexagonal rod, 

 which by means of an offset enters the four-sided pointed pyramid, c. In 

 the roof of the crown is fastened an octagonal elongated nut, perforated 

 longitudinally (with the roof) by a four-sided canal, corresponding to the 

 pyramid, c. The pyramid is slipped into the nut of the crown, and this 

 held at any position on the pyramid by means of a screw passing through 

 the side of the nut. The crown is cylindrical, with vertical angular grooves, 

 corresponding to the teeth cut on its cylindrical extremity. 



The hand trepan^ or trephine {fig. 6-1, crown 63 6c), consists of a perfo- 

 rator with movable central axis, handle, and screw. The handle, a, a, is of 

 ebony, three and a half inches long. It is perforated in the centre for the 

 reception of the shaft of the perforator. This shaft is hollow, and in it 

 plays a pointed centre pin, the extremity of which corresponds to the centre 

 of the circle of serrations, and which may be fixed at any point by a screw 

 in the shaft. 



The crowns of the perforator vary in shape. The old conical croion {fig. 

 65) is much like the next mentioned, and also provided with a centre pin, 

 but more conical and with fewer sharp ridges on the side. The conical ridged 

 crown {fig. 66) has the ridges equal in number and corresponding to the 

 teeth, but diverging from each other superiorly. The cijlindriccd ridged 

 crown {fiig. 67) has teeth forming right angled triangles, so arranged as only 

 to cut when turned in one direction. 



A peculiarly constructed instrument called KitteVe cranh trepan and cir- 

 cular saw is shown in fig. 68. The general features of the instrument will 

 be readily understood from a simple inspection of the figure, c represents 

 an arrangement by which the circular saw t can be employed, s is the 

 central pin or pyramid of the perforator. B, a key for screwing this in or 

 out. 



After the hair has been removed from the wounded part of the cranium, 

 three assistants stationed near, and the position of the patient settled, the 

 bone is next to be laid bare. This is done by making a T or V shaped or 

 oval incision, and reflecting the flaps. 



The perforation of the cranium comes next in order. The brace trepan 

 has here the advantage of the trephine. The centre pin or point of the 

 pyramid is made to project slightly beyond the cutting plane of the crown, 

 and is fixed by the screw. The operation is now to be commenced, and con- 

 tinued only until the teeth of the crown have made a well defined groove, 

 when the centre pin is to be withdrawn or pushed up. The operation is 

 then continued cautiously, care being taken to examine the groove fre- 

 quently with a probe to ascertain whether it has reached the dura mater. 

 To prevent splintering of the inner table of the cranium, the groove after 

 penetrating the cranium may be smoothed off with a knife having a knob 

 or button at the point (as shown in fi^. 10). 



015 



