CHAP. VIII - OF MECHANICAL ARRANGEME'NT IN THE HUMAN FRAME—OF THE BONES

Summary

We proceed therefore to propofe certain examples taken out of this clafs; making choice of fuch, as, amongft thofe which have come to our knowledge, appear to be the moft ftriking, and the beft underftood; but obliged, perhaps, to poftpone both thefe recommendations to a third, that of the example being capable of explanation without plates, or figures, or technical language.

OF THE BONES

I. I challenge any man to produce, in the joints and pivots of the moft complicated, or the moft flexible, machine, that was ever contrived, a conftruction more artificial, or more evidently, artificial, than that which is feen in the vertebræ of the human neck. Two things were to be done. The head was to have the power of bending forward and backward, as in the act of nodding, ftooping, looking upward or downward; and, at the fame time, of turning itfelf round upon the body to a certain extent, the quadrant we will fay, or rather, perhaps, a hundred and twenty degrees of a circle. For thefe two purpofes, two diftinct contrivances are employed. Firft, The head refts immediately upon the uppermoft of the vertebræ, and is united to it by a hinge joint; upon which joint the head plays freely forward and backward, as far either way as is neceffary, or as the ligaments allow: which was the firft thing required.