GABRIEL FALLOPIUS (1523 to 1562), the eminent anatomist of Modena, also a disciple of Vesalius, carried out accurate and successful researches in regard to the development of the teeth, and made them known in his book, _Observationes anatomicæ_, published at Venice in 1562, the year in which he died. His investigations enabled him to show the falsity of the opinion held by Vesalius, that the permanent teeth are developed from the roots of the temporary ones. He was, besides, the first who spoke in clear terms of the dental follicle. The teeth, says Fallopius,[288] are generated twice over, that is, the first time in the uterus, after the formation of the jaws, and the second time in extra-uterine life, before the seventh year. The first teeth are, at the time of birth, still imperfect, without roots, completely enclosed in their alveoli, and formed of two different substances; the part with which they must break their way out is osseous and hollowed; the deeper part, instead, is soft and humid and is seen covered with a thin pellicle, a thing which may also be observed in the feathers of birds when they are still tender. In fact, the part of the feather which comes out of the skin is hard and corneous, whilst the part which is embedded in the wings is soft and humid and has the appearance of coagulated blood or mucus. So also in the fetal teeth, the part corresponding to the future root presents itself like coagulated mucus. Little by little this soft substance hardens and becomes osseous, thus constituting the root of the tooth. Fallopius’ reference to the analogy between the development of teeth and that of feathers was highly important, as a point of departure for embryological researches which showed clearly the real nature of teeth, thus destroying the mistaken idea—held by Galen and many other authors—that these organs were bones.