Why have birds more varied motion in the neck than quadrupeds?
Because in birds the neck has a greater number of bones, and consequently of joints : the contrivance by which the spine of animals is rendered susceptible of varied motion, being by means of a strong chain of bones, (vertebrae) locked together by means of knobs and projections, to prevent dislocation, a chain which stretches from the head to the extremity of the tail. Except in the three-toed sloth, indeed, the bones in the neck of quadrupeds and of man are uniformly seven in number; the short-necked mole having the same as the long-necked giraffe ; in birds, the number is never less than nine, and varies from that to twenty-four.
