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THE SIXTEENTH CENTURV 175

The existence of the central chamber of the teeth appears to have
been unknown to Galen, as he does not allude to it in the least. Vesalius
was the first to put this most important anatomical fact in evidence. He
expresses an opinion that the central cavit\ facilitates the nutrition ot
the tooth. He sa\s, besides, that when a hole is produced in a tooth
by reason of acrid corrosive humors, the corrosion, when once the internal
cavity is reached, spreads rapidU and deeph in the tooth, owing to the
existence of the said cavit\-, and sometimes reaches even the end of
the root.
In the chapter in which Vesalius treats of the anatomy ot the teeth
(Chapter XI, p. 40), two ver\- well-drawn figures are found, one of which
represents a section of a lower molar, showing the pulp cavity and its
prolongation into the two root canals. The other represents the upper and
lower teeth of the right side, in their reciprocal positions, and shows very
clearh their general shape, the length of their roots, and the numberof these.
The changes which take place in the alveolus, after the extraction of
a tooth have not escaped the notice of Vesalius. He sa}s that after an
extraction the walls of the alveolus approach one another, and the cavity
is gradualh' obliterated.
Aristotle had affirmed that men have a greater number of teeth than
women. Vesalius declares this opinion absolutely false—although, after
Aristotle, it has been repeated by many other ancient writers—and says
that anyone can convince himself that the assertion of Aristotle is con-
trary to the truth, as it is possible for everybody to count his own teeth.
In spite of this, we find the above-mentioned error even in writers
subsequent to Vesalius; for example, in Heurnius (professor at Le\den
toward the end of the sixteenth century), who expresses an opinion
that rarely do women have thirty-two teeth, like men.
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, medul-
lary roots ; and the part of the tooth which appears above the gums is
united to the root, so to sa\-, 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 actuallx
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 especialU' 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.