In the great work of Vesalius the anatomy of the teeth is unfortunately treated with much less accuracy than that of the other parts of the body. However, his description of the dental apparatus[283] is far more exact than that of Galen, and represents real progress. The number of the roots of the molar teeth (large and small) is indicated by Galen in a very vague and inexact manner, since he says that the ten upper molars have generally three, sometimes four roots, and that the lower ones have generally two, and rarely three. Vesalius, having examined the teeth and the number of their roots in a great number of skulls, was able to be much more precise. In regard to roots, he makes, for the first time, a very clear distinction between the premolars next to the canine (small molars) and the other three, and says that the former in the upper jaw usually have two roots, and in the lower, one only, whilst the last three upper molars usually have three roots and the lower ones two. As everyone sees, these indications are, in the main, exact. Other important facts established by Vesalius are as follows: The canines are, of all the teeth, those which have the longest roots. The middle upper incisors are larger and broader than the lateral ones, and their roots are longer. The roots of the last molars are smaller than those of the two preceding molars. In the penultimate and antepenultimate molars, more often than in the other teeth, it sometimes happens that a greater number of roots than usual are found, it being not very rare to meet with upper molars with four roots, and lower ones with three. The molars are not always five in each half jaw; sometimes there are only four, either on each side, or on one side only, in only one jaw or in both. Such differences generally depend on the last molar, which does not always appear externally, remaining sometimes completely hidden in the maxillary bone, or only just piercing with some of its cusps the thin plate of bone which covers it; a thing which Vesalius could observe in many skulls in the cemeteries. In regard to the last molar, the author speaks of its tardy eruption and of the violent pains which not unfrequently accompany it. The doctors, he adds, not recognizing the cause of the pain, to make it cease have recourse to the extraction of teeth, or else, attributing it to some defects of the humors, overwhelm the sufferer with pills and other internal remedies, whereas the best remedy would have been the scarification of the gums in the region of the last molar and sometimes the piercing of the osseous plate which covers it. This curative method, of which no one can fail to recognize the importance, was experimented by Vesalius on himself, in his twenty-sixth year, precisely at the time that he had just begun to write his great treatise on anatomy.