To reach the _foramen ovale_ (third division), the needle is introduced through the cheek behind the last molar tooth, at the lower border of the zygoma, at a point 2¹⁄₂ cm. in front of the descending root of the zygoma. The blunt needle penetrates the masseter muscle and the posterior part of the temporal muscle. It is then directed backwards and slightly upwards till it impinges on the skull at the external pterygoid plate. It is then pushed on, upwards and backwards, till it enters the foramen ovale at a depth usually of about 4 cm. from the zygoma. In case of difficulty in passing the needle through the sigmoid notch of the jaw the mouth should be widely opened. If the needle be directed too low it may penetrate the pharyngeal wall or the Eustachian tube; if too far back, the middle meningeal artery. To reach the _foramen rotundum_ (second division)--a rather more difficult procedure--it is necessary to find the posterior border of the orbital process of the malar bone, prolonging this line downwards to the lower border of the zygoma and inserting the needle ¹⁄₂ cm. posterior to this point. The needle is pushed horizontally inwards and the point directed slightly upwards, the foramen being reached in the pterygo-maxillary fossa at a depth of about 3 cm. from the zygoma. The needle, for an average-sized skull, should never penetrate deeper than 5 cm. The structures pierced are the anterior fibres of the masseter and the buccinator muscles. If directed too horizontally, the needle will pass below the nerve and reach the spheno-palatine region; if too high, the sphenoidal fissure may be reached and the branches of the third nerve damaged, causing diplopia and dilatation of the pupil. To reach the _sphenoidal fissure_ (first division), the needle is introduced at the outer margin of the orbit, close within the fronto-malar articulation, and passed along the outer wall of the orbit to a depth of 3¹⁄₂ to 4 cm. Needless to say, it is essential that these injections to the basal foramina should only be carried out in the first instance after experimentation on the cadaver. In each case a single injection may suffice, but as a general rule it is advisable to repeat the process after two or three days, and again at longer intervals. It is not necessary that the nerve-trunks should be pierced, but better results are obtained by so doing. The surface area to which the particular nerve-trunk is distributed immediately becomes anæsthetic, remaining in that state till the effect of the injection shall have passed off. The masticatory muscles are paralysed. The injection may be followed by paresis of the facial muscles, by œdema of the lower lid, and by hæmatomata. These last-named results are, however, transitory. =Results.= Schlösser, who injects 15 to 20 minims of an 80 per cent. solution of alcohol, reported in 1907 that he had treated 123 cases, the average period of relief from pain being ten and a half months.