Among the authors previous to, or contemporaries of, Eustachius, some affirmed that the sensibility of the tooth resides in the pellicle which lines its inside cavity, others in the membrane which, like periosteum, clothes the root of the tooth, others in both these parts. Eustachius does not show himself more partial to the one than the other of these opinions; he is, however, firmly persuaded that the hard substance of the tooth is also endowed with sensibility. Though it is not easy to explain how this may be, he considers it probable that the nerve, fraying itself out inside of the tooth in minute filaments at the time when the substance of the tooth is still soft and mucous, intermixes intimately with it, thus communicating to it the faculty of feeling, which then persists in it, even after the ossification of the tooth. Such an hypothesis is certainly worthy of the lofty intellect of Eustachius, and has in itself, so it seems to me, something of truth. In the two following chapters,[295] the author speaks in a masterly and admirable manner of the functions of the teeth and of their utility. Among many other true and interesting observations, he remarks that by the loss of their teeth even the most powerful dogs become cowards. Besides what concerns the human teeth, excellent notions of comparative anatomy, above all in what regards the monkey, the dog, and the ruminants, are to be found in this little but most precious book of Eustachius. The teeth, says he, are not equally hard in all animals, and many ancient authors have affirmed that ferocious animals have much harder teeth than tame ones. Chapter XXIX, relating to dental anomalies, is one of the most interesting. We here quote the greater part of it. “Some historians relate that Pyrrhus, King of Epirus, Eurifeus, of Greece, and many others, had, instead of teeth, a continuous bone, furrowed by somewhat deep vertical lines, in no way different from what one sees in the multiple molars of the goat. It has never happened to me, says Eustachius, to witness a similar union of all the teeth; I have, however, sometimes observed continuity between three or four molars, precisely in the same manner as in sheep. It also once happened to me to observe in the case of an old man, a fellow citizen of mine, that the teeth were covered up on every side by a hard and almost stony substance, and no longer exhibited any trace of separation, offering instead the appearance of a single bone.” “One reads that Timarchus, of Cyprus, had two rows or series of teeth and Hercules three.”