Page:Popular Science Monthly Volume 4.djvu/273

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tological research, and the expression is probably a figurative one, as observed by Dr. Buckland. Serpents progress by the "foldings and windings they make on the ground," and the stiff, movable scales which cross the under portion of the body; but the windings are side-ways, not vertical.

Fig. 2.
PSM V04 D273 Ringed Boa.jpg
Aboma, or Ringed Boa.

The structure of the vertebræ is such, that upward and downward undulations are greatly restricted, and many illustrations, showing sharp vertical curves of the body, are exaggerations. Most persons have seen snakes glide slowly and silently, without any contortion. They seem to progress by some invisible power; but, if permitted to move over the bare hand, an experiment easily tried, a motion of the scales will be perceived. These are elevated and depressed, and act as levers, by which the animal is carried forward. Nor can a serpent progress with facility on the ground, without the resistance afforded by the scales. It is stated that it cannot pass over a plate of glass, or other entirely smooth surface. We saw the experiment tried, by