The Antrum Of Highmore presents three walls, a roof, and a floor. The anterior, or facial wall, is limited externally by the malar ridge, and below by the alveolar border. It is thin, and presents a prominence for the canine tooth, which is separated from the molar ridge by the canine fossa, and the infra-orbital canal, which transmits the infra-orbital vessels and nerves. The position of the latter may be defined by taking a point on Holden's line (drawn from the supra-orbital notch to the internal between the bicusp teeth of both jaws), inch below the lower orbital margin. The nasal wall forms the outer boundary of the inferior and middle meati. The portion bounding the inferior meatus is osseous, and is thinnest immediately beneath the attachment of the inferior turbinate, where, at a point inch behind its anterior extremity, the antrum is best tapped from the nose. Above the inferior turbinate the wall is partly osseous and partly membranous, and presents the ostium, which opens into the antrum close to its roof, and into the nose at the most dependent portion of the infundibulum. It therefore follows that suupurative processes in the frontal sinus or anterior ethmoidal cells are very apt to secondarily infect the antrum of Highmore, the pus travelling down the naso-frontal duct to the infundibulum, and thence through the maxillary ostium. Once the pus enters here, it does not readily escape, owing to the position of the ostium, save when the head is laid on the opposite side, the pus then frequently coming away in a gush. The ostium varies in size, but averages 1/8 inch vertically and inch antero-posteriorly. Not infrequently an accessory ostium is present, and is sometimes the larger of the two. When present it is situated below the other, and facilitates the escape of pus into the throat. Neither ostium is easily reached from the nares by catheter.

The roof forms the floor of the orbit, is thin, and presents the canal from the superior maxillary nerve and vessels. This canal is sometimes invaded or crushed in antral disease, giving rise to severe neuralgia, while later the tumour or pus may invade the orbital cavity or ethmoidal cells. The floor is the alveolar border of the superior maxilla, and is on the same level as the nasal floor. The bone is generally thinnest over the fangs of the first and second molars, while the fang of the canine generally lies in front of the antrum. Probably the second molar bears the most constant close relation to the antrum, a point to bear in mind in entering the antrum from the mouth. Disease of the fangs of the molar teeth sometimes gives rise to antral suppuration. The antrum varies much in size, and, where small, the walls, particularly the alveolar, are thicker, and vice versa. When large the cavity may extend mesially into the palatal plate of the maxilla. The walls are supplied by blood from the periosteum, which lines both the inner and outer surfaces, and from the walls numerous septa pass into the cavity, thus partially subdividing it. This subdivision, combined with the position of the ostium, renders antral suppuration, as a rule, intractable. It has already been stated that the antrum may be reached through the nose or through the socket of one of the molars. Probably the most efficient mode of dealing with antral suppuration, however, is to evert the upper lip, cut through the junction of gum and lip, and shell all the tissues upwards with a periosteal elevator until close to the infra-orbital foramen, when an opening can be made by trephine or simply crushing in the canine fossa. This opening may be sufficiently large to permit of thorough exploration and removal of disease, but if a permanent opening be required, it is best made through the nose.