Page:Natural History, Reptiles.djvu/75

Rh "The passage from the Lizard tribe to the Serpents," observes Mr. Bell, "is by a succession of very gradual modifications of development. In the lower forms of the Saurian group, the body becomes gradually elongated and serpentiform: its ribs increase in number, the anterior and posterior limbs are removed farther and farther from each other, and diminish in size and power, exhibiting in some forms the anterior, and in others the posterior only, external to the integument, until at length they cease to appear, being merely rudimentary, and wholly covered by the skin. Of this transition state we have an example in the common Slow-worm (Anguis fragilis), which, though completely serpentiform in its external, appearance, yet possesses the minute rudiments of limbs entirely concealed under the integuments. Notwithstanding this general form of the Serpent, they have not the expansible jaws of the true Serpents: nor is the character of the ears the same, the tympanic membrane not being superficial, nor the auditory passage covered by integument; the eyes, also, like those of the Lizards, are furnished with moveable eyelids, which are wholly wanting in the true Serpents."

"The movements of the Saurian reptiles are effected principally by means of their feet, and in some of the higher forms exclusively so; but as they descend towards the more elongated form of the Skinks and other genera, in which these organs become more and more subordinate, they are greatly assisted by the lateral motion of their bodies, different parts of which are brought into alternate contact with, and pressure upon either the roughness of the ground or the shrubs and herbage