On Fleshes

​13. And for this reason teeth grow later than the other parts: in the lower jaw there are hollow veins, and to this bone alone of the bones do they provide nourishment. And bones yield such growth as they themselves are, and indeed all other things return such growth as they themselves are. For indeed the veins from the stomach and the intestines, into which food and drink gather, when these are heated, draw the finest and wettest part; the thickest part of it is left behind, and becomes feces in the lower intestines; and the finest part the veins draw from the stomach and the intestines above the jejunum, while the food is being heated. But when it passes the jejunum, it turns into the lower intestines and becomes feces. And when the nourishment arrives at each part, it yields such form of each as it was; for irrigated by the nourishment each part grows: the hot, the cold, the glutinous, the fatty, the sweet, the bitter, the bones, and all other things whatsoever that are in man. For this reason teeth grow later. And it has been said by me before that the jaws alone of the bones have veins themselves in themselves; and because of this, more nourishment is drawn than into the other bones. And having more nourishment and a more concentrated influx, they generate growth from themselves of such a kind as they themselves are, as long as the whole human is growing. And it grows when it becomes conspicuous; and it becomes most conspicuous from seven to fourteen years of age, and in this time the largest of the teeth grow and all the others, when those have fallen out which came from the nourishment in the womb. And growth continues also into the third seven-year period, in which one becomes a youth, up to four and five seven-year periods; and in the fourth seven-year period, teeth grow, two for most people, and these are called wisdom teeth.

​14. And hair grows in this way: there are bones and the brain, from which such growth comes, because there is none of the surrounding glutinous, as there is for the ligaments, and of the fatty; for if the fatty had been present, it would have been burned out by the heat. But perhaps someone might wonder why there is also much hair in the armpits and on the pubes and on the whole body: the same account holds for this. Wherever the glutinous happens to be in the body, there hair is formed by the heat.

​15. And one hears for this reason: the passages of the ears reach to a bone that is hard and dry like a stone; and in this bone, there is naturally a spongy cavity. And sounds strike against the hard part, and the hollow bone resonates through the hard part. And the skin near the organ of hearing, against the hard bone, is thin like a spiderweb, the driest of the rest of the skin. And there are many proofs that what is driest resonates most; and when it resonates loudest, then we hear best. And there are some who said, writing on nature, that the brain is what resonates; but this could not be. For the brain itself is wet, and the membrane around it is wet and thick, and around the membrane are bones. Nothing wet, therefore, resonates, but dry things do; and things that resonate produce hearing.