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. 68, consists of a handle part, b, 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 pdssing 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 (jig. 64, crown 68 bc), 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 crown (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 cylindrical ridged 
crown (fig. 67) has teeth forming right angled triangles, so arranged as only 
to cut when turned in one direction. 
A peculiarly constructed instrument called Kittel’s crank trepan and cir- 
cular saw 1s shown in fig. 68. The general features of the instrument will 
be readily understocd from a simple inspection of the figure. c represents 
an arrangement by which the circular saw ¢ 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 eutting 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 detined 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 fig. 10). 
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