_Horsley’s nibbling or rongeur forceps._ This instrument is mainly utilized in the smoothing and refreshing of sharp edges of bone, and in the ‘morcellement’ of the thinner portions of the skull--temporal and cerebellar regions. _De Vilbiss’s forceps._ A clever contrivance whereby the operator is enabled to cut a narrow channel in the bone. Mainly utilized in the formation of the osteoplastic flap. =Craniotomy.= Craniotomy, or osteoplastic resection of the skull, was first carried out by Wagner. It is proposed to describe that method only which, by experience, has been found to meet all requirements--the formation of the osteoplastic flap by means of the hand-trephine, Gigli’s saw, and de Vilbiss’s forceps. The protective gauze dressing and scalp-tourniquet are applied as before. A large ______ \ / -shaped \ / incision is made in such a manner as to include the area which it is desired to expose. The two vertical limbs of the incision should converge to such a degree as to allow of the subsequent ready fracture of the flap along its base. The knife is entered at one extremity, carried down to the bone, and the three incisions rapidly made, one after the other. Along the line of each of the three incisions, the pericranium is stripped away from the bone so as to allow of adequate exposure. At the anterior and posterior angles of the flap the tissues are retracted a little more, permitting the application of a half-inch diameter trephine. Here the two trephine-holes are bored--with the usual precautions against damage to the dura mater--and the two disks of bone elevated and removed. Between these two trephine-holes the dura mater is separated from the bone and the special director introduced, entering at the one hole, emerging at the other, and lying throughout between the dura and the bone. The saw is now passed along the groove of the director, the handles affixed, and the bone intervening between the two trephine-holes divided, not straight out to the surface, but bevelled or cut in such an oblique manner that the bone-flap, when replaced, rests on a ledge (see Figs. 17-19). The sawing process generates considerable heat, and the assistant should be instructed to keep up irrigation with saline solution or sterilized water. The sawing is carried out by steady side-to-side traction, without jerks; if the saw breaks, the special handle may be attached, thus obviating the necessity of introducing a new saw. [Illustration: FIG. 17. FIRST STAGE IN THE FORMATION OF AN OSTEOPLASTIC FLAP. Gigli’s saw, protected from the dura mater by the special director, passing between the two trephine-holes. For further description, see text.] [Illustration: FIG. 18. SECOND STAGE IN THE FORMATION OF AN OSTEOPLASTIC FLAP. The bone-flap turned down and the dura mater exposed.]