. Human physiology : designed for colleges and the higher classes in schools, and for general reading. hich the nerve of smell isexpanded. A representation of these cavities is given in ; in which a is the mouth;b, the opening into the nos-tril ; d, a part of the base ofthe skull; c, the communica-tion of the nostril with theback of the throat; e, the cur-tain of the palate; I, the front-al sinus ; m, another large si-nus ; g, i, A, spongy bones pro-jecting into the cavity of thenostril. There is a large sinus,that is not seen in this figure,which lies over the teeth inthe jaw-bone. The
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. hich the nerve of smell isexpanded. A representation of these cavities is given in ; in which a is the mouth;b, the opening into the nos-tril ; d, a part of the base ofthe skull; c, the communica-tion of the nostril with theback of the throat; e, the cur-tain of the palate; I, the front-al sinus ; m, another large si-nus ; g, i, A, spongy bones pro-jecting into the cavity of thenostril. There is a large sinus,that is not seen in this figure,which lies over the teeth inthe jaw-bone. The differentsinuses are lined with the mu-cous membrane extending into them from the nose. These, withthe spongy bones make a very large extent of surface in thecavities devoted to the sense of smell. The branches of thenerves of smell enter these cavities, to be distributed overthin walls, through many small openings in a bone in theroof of the nose, giving it a sieve-like appearance. 280. The lower jaw is a bone shaped something like ahorseshoe, with its ends turned considerably upward. It has two. INNER BONES OF THE NOSE. THE BONES. 181 Structure of teeth. Three different kinds of texture. smooth projecting surfaces which articulate with two corres-ponding shallow cavities in the temporal bone. Its prominenceat the lower part in front, the chin, is peculiar to man, therebeing no such prominence in any other animal. The lowerjaw has sockets for the teeth, and it is so constructed, and iaso arranged with muscles, that these teeth can be brought tobear against the teeth of the upper jaw in cutting and grind-ing motions. 281. The teeth are very nearly like the bones in , but they differ from them in some particulars whichit will be interesting to notice. Every tooth has in it three dis-tinct structures, which differ in hardness, for reasons which willappear clear to you as I proceed. The dentine or ivory constitutes the body both of the tooth and of its fangs. In th
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