Although the author does not express himself very explicitly, he seems to consider the follicle of the tooth substantially identical with its ligament. “This is at first mucous, but afterward, becoming more consistent, causes the tooth to adhere to the socket and gum very firmly, as if it were glued.” “As the part of the tooth which comes out of the gum projects from the aperture of the follicle like a gem from its bezel, so—says Eustachius—some believe that the crown of a temporary tooth is a mere appendix, and that the follicle comes out of its concavity through a dividing line which they imagine to exist between this supposed appendix and the remaining part of the tooth. But assuredly those who assert such things show that they have studied the anatomy of the teeth so carelessly that, by this one error, they make manifest their great ignorance together with their great temerity.[290] The line which is observed on the tooth on the part corresponding to the adhesion of the gingival margin and of the dental ligament is very superficial, and after having scraped it away, there does not remain any trace of a division. But apart from this everyone can very easily observe, even in infants, or in kids, that the tooth when ossified does not present any line of division and that the still mucous follicle envelops it freely, and may be easily separated from the tooth; which would not be the case, if the follicle issued from between the tooth and its supposed appendix.” Thus, Eustachius declares entirely false the opinion already expressed by Celsus, that the permanent tooth grows from the root of the milk tooth. He affirms clearly and decisively that between the external and the radical part of a milk tooth no real division exists, and that the ossification of the tooth, beginning from the crown, proceeds without any interruption right down to the end of the root. If it were true, says he, that in children only the imaginary epiphysis or appendix falls, and that the new tooth is substantially represented by the remaining part of the first, it could never happen, as instead it often does, that the new tooth appears before the first one falls. Besides, between the lower part of the first tooth and the upper part of the second no correspondence exists either in size or shape, as ought necessarily to be the case if the two parts were joined together. This is not all; the lower part of the temporary tooth is perforated, and receives in its interior bloodvessels and nerves, whilst the upper part of the permanent tooth is quite massive and imperforated. How, then, could this second tooth transmit bloodvessels and nerves into the cavity of the first? Again, how could the continuity of these bloodvessels and nerves with their respective branches be possible, if an imperforate body, such as the crown of the permanent tooth, were really interposed?