There is no doubt that the existence of the maxillary sinus was already known before Highmore, the celebrated anatomists Vesalius, Ingrassias, Eustachius, and Fallopius having spoken of it very clearly; only through ignorance of the history of anatomy has it been affirmed by many that this cavity was discovered by Highmore, to whom is only due the merit of having described the maxillary sinus, by him called _antrum_, most accurately, and of having made known the possibility of a communication between it and the mouth. Highmore calls attention to the fact that the inferior wall of the antrum often presents small projections, which correspond with the tops of the alveoli, and that the osseous lamina which interposes between these latter and the maxillary sinus is often extremely thin; for which reason, it may easily happen that, in extracting one of the teeth below the cavity, one may bring away together with the tooth the small osseous plate that forms the bottom of the alveolus, thus leaving the maxillary sinus open at its inferior part. With regard to this, he refers to a most interesting case which afterward acquired a high degree of notoriety. It relates to a lady who had suffered from toothache for some years, and who from time to time had had several decayed teeth extracted, without, however, finding relief. The pain only ceased after the patient had had the left upper canine removed. But after this operation an incessant flow of humors from the alveolus of the extracted tooth took place. The patient, in great anxiety at this circumstance and desirous of seeing clearly into the causes of it, herself explored the affected part with a silver probe, the entire length of which penetrated into the cavity, producing in the patient the effect of its having reached the eye. Still more amazed, and urged on by the desire of becoming still better acquainted with the extent of the evil, she now made use of a long feather, which she had previously stripped, and discovered to her painful surprise that this new instrument of exploration entered to so great a distance that it, according to her idea, penetrated into the skull. From this she derived argument for the belief that the morbid phenomenon had its origin in her brain. Believing herself affected with a serious malady, she consulted Highmore, who had the satisfaction of being able to tranquillize her completely by making her understand that the jaw bone is hollow in the inside, and that its cavity had remained open underneath in consequence of the extraction of the canine tooth; and also, that the feather had not penetrated to such a distance as she supposed, but had curved inside the bone. As to the discharge which had given so much trouble and alarm, Highmore considered it quite a natural circumstance, derived simply from the opening of the antrum, as he held that in many cases the maxillary sinus contains mucus, and that this condition was, therefore, altogether normal.