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of all the bones, grow in length during a man's whole 

 'life: which is providently designed, to repair the 

 waste that is continually miide by attrition : 2. That 

 the teeth are the only bones which are not covered 

 with that exquisitely sensible membrane, the perio- 

 steum : 3. That they are harder and firmer than any 

 other bone, that they may be more durable and fit ti> 

 chew the most solid aliments: 4. That for their nou- 

 rishment, there is a cavity contrived in each side of 

 the jaw-bone, in which are lodged an artery, a vein, 

 and a nerve, which through smaller cavities send their 

 twigs to e?ery tooth : 5. That as infants are designed 

 to liyeon milk, for some months, they are so long 

 without any teeth : whereas animals that need them, 

 have them sooner, and some are even born with them. 

 6. The different shape of the teeth is remarkable. 

 The fore- teeth are formed broad, and with a thin and 

 sharp edge, like chissels, to cut oif a morsel from any 

 solid food. The next, one on each side, are stronger, 

 deeper-rooted, and more pointed, to tear tougher ali- 

 ments : the rest are made flat and broad at top, and 

 withal, somewhat uneven, that thereby they may the 

 better retain, grind and mix the aliment. 7. Because 

 biting and chewing require much strength, partly in 

 the teeth themselves, partly in the instruments that 

 move the lower jaw r 5 which alone is moveable ; nature 

 has given it strong muscles, which make it bear forci- 

 bly against the upper jaw : and has not only fixed 

 each tooth in a distinct cavity, as in a close, strong 

 and deep socket, but has given holdfasts to the seve- 

 ral sorts of teeth, suitable to the stress that is to be 

 laid upon them. So whereas the cutters* and eye-teeth 

 have only one root, the grinders, designed tor harder 

 work, have three: in the upper jaw otten fonr, be- 

 cause they are pendulous, and the substance of the 

 jaw somewhat softer. 8. The situation of the teeth is 

 most convenient. The grinders are behind, near the 

 centre of motion, because chewing requires a consi- 

 derable force : the cutters before, ready for their easier 

 work. 



