process of the lower jaw with the temporal tendon attached to it. The latter structure is cut through close to its attachment to the bone, or the coronoid process is sawn through, and the whole of the temporal muscle is turned upwards and kept out of the way with a retractor. This exposes the lateral wall of the skull just above the pterygoid ridge, and the pin of a one-inch trephine is applied at this level opposite to the centre of the zygoma and a circle of bone removed (see Fig. 217).

The removal of the crown of bone must be effected with great care, as a wound of the dura mater, which it is important to avoid,

may occur

FIG. 218.-PUNCH FORCEPS FOR CRANIAL OPERATIONS. These forceps can be used in very restricted areas and are useful in enlarging the trephine hole downwards towards the base of the skull.

very easily owing to the variability in the thickness of the skull. When the crown of bone has been removed, the opening is enlarged in all directions, but especially downwards with cutting pliers or gouges (see Fig. 218). The foramen ovale is identified by detaching some of the fibres of the external pterygoid muscle and finding the third division emerging from it, and the bone between it and the opening in the skull is cut away as freely as possible. At this stage there is generally free bleeding from the pterygoid plexus of veins, but this soon yields to firm sponge pressure.

The dura mater is next separated from the floor of the middle fossa

of the skull and raised along with the brain above it, and the ganglion looked for. During this stage of the operation a powerful electric forehead lamp is a necessity; the ganglion lies so deep, and the wound is so often obscured with blood that the structures cannot be identified clearly without a good light. The dura mater is separated by sweeping a blunt instrument around the edge of the opening in the skull between it and the bone, and raised with broad retractors until the floor of the middle fossa is well exposed (see Fig. 220). The dura mater is pushed gradually upwards and inwards, the brain being gently moulded into its new position and not violently compressed. The only complication likely to be met with at this stage is injury to the middle meningeal trunk as it emerges from the foramen spinosum, but with care this can

ALLEN & HANBURYS

FIG. 219.-CRILE'S DEPRESSOR. The pledgets of gauze are kept in place by the ring-like end of the depressor. The shank is fine and does not get in the way.

usually be avoided; should it be necessary to divide the artery, the best plan is to cut it across between ligatures about half an inch from the foramen. Should the vessel be torn just as it passes out of the foramen, the bleeding is apt to cause trouble; if the lower end of the artery can be seized in forceps, it should be twisted and pushed into the foramen spinosum. Failing this, Horsley's wax may be applied to the foramen.

When the dura mater has been lifted well up, the surgeon will recognise the third division of the trigeminal nerve passing almost vertically downwards from the Gasserian ganglion to the foramen ovale which lies internal to, and a little in front of, the foramen spinosum, and it is here that the serious difficulties of the operation begin. The best procedure is to define the nerve clearly with a fine dissector, and then to cut it across with a pair of fine scissors or a tenotome; the divided end is seized in a pair of

fine Spencer Wells's forceps and serves as a safe guide to the ganglion. The surgeon now proceeds to identify the remaining divisions of the nerve, a proceeding requiring great care owing to the proximity of the cavernous sinus. By detaching the dura mater inwards towards the middle line, the foramen rotundum is identified with the second division passing through it; the smaller ophthalmic division lies above it. The sixth nerve is also brought into view, lying above and parallel to the second division and must be carefully protected from injury. During the whole of this stage the operator is likely to be much hampered by the free and continuous oozing that takes place from the small veins joining the cavernous sinus; this must be arrested by pressure, small pieces of sponge upon long-handled forceps being thrust down into the bottom of the wound and held there for a short time. An excellent instrument devised by Crile for this purpose is seen in Fig. 219. Small pledgets of gauze are packed down on to the bleeding points and held firmly in place by the depressor, which does not get in the operator's way and only applies the pressure where it is needed.

When the branches of the nerve have been identified, the surgeon proceeds to find and remove the ganglion itself. To do this, the divided. end of the third division is traced back to the ganglion where it lies in a compartment in the dura mater at the apex of the petrous portion. In freeing the ganglion the dura mater may be opened, but this is not a serious accident; indeed, it facilitates the operation somewhat, as it allows the dura mater to collapse and so gives better access to the ganglion. The edge of the ganglion is separated behind with a fine dissector and it is then raised from its bed-if necessary with a few touches of a tenotome-and seized firmly in strong forceps. With these it is partly pulled and partly dissected away from behind forwards. It is generally recommended that the motor root of the ganglion, as well as the first division, should be left untouched; no doubt this is advisable if it can be done, but there is generally so much oozing that accurate differentiation is not easy, and in that case it is best to cut across the third division-and with it the motor part-early in the operation. As the ganglion is detached and pulled forwards, the second division is lifted away from the outer wall of the cavernous sinus to which it is closely adherent, and thus damage to this important structure is avoided. Finally this nerve is cut off flush with the foramen rotundum and the ganglion comes away, the ophthalmic division being often torn across in the process. The venous oozing will generally cease directly the dura mater is allowed to fall back into place, and it will rarely be necessary to put a drainage tube into the cranium and, still more rarely, to plug the wound with gauze to arrest bleeding. This latter step may be necessary, however, should the cavernous sinus be wounded in the later stages of the operation; the bleeding then is most profuse. There is no need to fasten either the divided zygoma or the temporal tendon into place, if the motor root of the nerve has been

divided, since both the temporal and masseter muscles will be paralysed. The flap is sutured accurately in place, a fine drainage tube being inserted at one of the lower angles.

The chief danger in the operation is a wound of the cavernous sinus which is indicated by furious bleeding at the time and, perhaps, by thrombosis of the sinus afterwards. Injury of the third, fourth, and

up by a broad flexible spatula. It usually requires the use of a forehead lamp to
distinguish the ganglion and the three branches of the nerve.

sixth nerves, with resulting widespread ocular paralysis, may also occur, as a result of rough handling in the later stages of the operation or of cavernous sinus thrombosis.

After-treatment. The patient is put back to bed with the head somewhat raised, in order to restrain hæmorrhage and to diminish intra-cranial tension. The eyelids should be looked at daily and irrigated with warm boric lotion, after which they are dried and a sterilised dry cotton-wool

pad is bandaged on. The stitches uniting the lids are removed on the fifth day, but for several weeks afterwards the greatest care must be taken to prevent irritation of the anæsthetic conjunctiva; to this end the patient should use a boric eye-wash frequently and the eye should be covered with a shade. In spite of all precautions, however, trophic ulceration of the cornea (neuro-paralytic keratitis) may supervene and the globe may have to be excised. The drainage. tube should be removed at the end of forty-eight hours. The wound heals well and there is hardly any risk of injury to the brain subsequently, as the defect in the skull is quite low down.