The head of a horse has been divided below the orbits, and a back view of the facial portion is here shown, the spectator being supposed to look into the cavities, which have been thereby exposed. _a_ indicates the molar teeth on that side which was not the seat of disease, and they are of the natural length and obliquity. _b_ denotes the teeth on that side where the disease was seated, and shows them to be not only unusually slanting on their grinding surfaces or tables, but also of considerable length. It was the last tooth on this side which was carious, and the shape of the molars has been occasioned by the animal during its life, being unable, because of pain, to freely use these organs in chewing its food. The effort to avoid any stress upon the diseased tooth, has caused those on the same side to suffer only partial attrition; hence they have become long and slanting, presenting sharp pointed edges, which lacerated the lining membrane of the mouth. The incisors, a distant view of which is given, likewise display the consequence of the animal's mode of feeding. Turning from the teeth to the exposed cavities above them, it will be seen that these are not symmetrical, or of equal dimensions, which in the head of a healthy subject, they undoubtedly ought to be. Those on the diseased side are not only the largest, but differently formed. The alteration has resulted from the inflammation and accumulation of pus within them. Something besides pus, however, has been thrown out. _e_ represents the healthy maxillary sinus as an empty space: _d_ is the like part, but it is here filled by a fine cellular structure composed of bone, which has been produced by the action of disease. The plates which form the cells are delicately thin, and beautifully arranged: the little cavities were once full of a thick and sanguineous matter, and the larger spaces above them contained a very fetid but almost solid substance, which was pus, that, by being pent up, had become of a cheesy consistency. _c_ indicates the nasal division, or cartilaginous wall, which separates the two chambers of the nose. As will be observed, it has been forced on one side by the enlargement of the affected parts.