We find but little in Vesalius concerning the development of the teeth. He, indeed, made some observations and researches on this point, but these, from their insufficiency, led him to quite mistaken conclusions. The teeth of children, he says, have imperfect, soft, and, as it were, medullary roots; and the part of the tooth which appears above the gums is united to the root, so to say, as a mere appendix, after the fall of which there grows from the root the permanent tooth. This error arose in the mind of Vesalius from observing that when children lose their milk teeth, these have the appearance of a kind of stump, as if the root had actually remained in the socket. Besides this, he had observed with what facility the milk teeth fall out; and he here calls to mind that, when about seven years old, he himself and his companions used to pluck out their loosened teeth, and especially the incisors, with their fingers, or with a thread tied around the tooth. The softness of the dental roots in children, the easy fall of the milk teeth, and the want of the lower part of the roots in these, must have raised the idea in his mind that the roots of the milk teeth remained in the socket, and that the upper part of the temporary teeth, instead of being a continuation of the root, was joined to this as a simple appendix, and in a very weak way, as though designed to remain in place for a limited length of time only. In Vesalius[284] is found a dental terminology—Latin, Greek, Hebrew, and Arabic—which affords some interest. The incisors are called in Latin _incisorii_, _risorii_, _quaterni_, _quadrupli_; and the two middle incisors have been denominated by some authors _duales_. The canines are called in Greek kynodontes, which means the same as the Latin _canini_, dog’s teeth. In Latin they have been also denominated _mordentes_, and by some also _risorii_, a name which by others is given to the incisors, as we have already seen. The molars have also been called in Latin _maxillares_, _paxillares_, _mensales_, _genuini_.[285] But some authors give this last name only to the last molars, or wisdom teeth, _dentes sensus et sapientiæ et intellectus_. These teeth have also been called _serotini_ (that is, tardy), _ætatem complentes_ (that is, completing the age, the growth), and also, in barbaric Latin, _cayseles_ or _caysales_, _negugidi_, etc.