[Illustration: FIG. 90. TO ILLUSTRATE THE OPERATIONS ON THE GASSERIAN GANGLION. s.f., sphenoidal fissure; f.r., foramen rotundum; f.ov., foramen ovale; s.s., Frazier’s operation on the sensory root. The dotted line = the line of section in removal of the lower two-thirds of the ganglion (_Jonathan Hutchinson’s operation_). The shaded portions = parts removed in intracranial resection of the second and third divisions of the nerve (_Abbé’s operation_).] The temporal fascia is next incised--slightly below the line of the skin incision. Finally, the temporal muscle is divided--again at a lower level than the fascial incision. Skin, fascia, and muscle are then turned down to a zygomatic base. Some surgeons split the temporal muscle in the direction of its fibres, a course, however, that tends somewhat to cramp the operative field. The trephine is applied to the bone, the surgeon aiming at striking the angle between the anterior and posterior branches of the middle meningeal artery. The bone-disk is removed. With the aid of craniectomy forceps the bone is nibbled away, more especially in the downward direction towards the base of the skull. It is essential that the operator should get down as low as possible, for the lower the line of attack the easier the approach to the ganglion and the less the damage incurred by the brain (from retraction). The opening in the bone, oval in shape, should present a diameter in the vertical direction of about 1 to 1¹⁄₄ inches, and an antero-posterior diameter of about 1¹⁄₂ inches. The dura is stripped away from the base of the skull, partly with the fingers and partly with the blunt dissector, and a flat, slightly malleable retractor introduced along the floor of the middle fossa, the dura and overlying temporo-sphenoidal lobe being gently lifted upwards. The surgeon should take upon himself the responsibility of retracting the brain, holding that instrument with the one hand and working inwards with the other, directing his course towards the foramen spinosum (middle meningeal) and foramen ovale (third division of the fifth nerve). During this stage hæmorrhage, derived mainly from the branches of the middle meningeal, is often troublesome. It may be controlled by the insertion of dry or wet gauze--in the latter case the gauze is soaked in saline solution or sterilized water (at a temperature of about 110° Fahrenheit)--or by the introduction of cotton-wool plugs to each of which a silk thread is attached, for the purpose of facilitating their final removal.