288 CLASS REPTILIA. 



that, although deprived of feet, they are enabled to spring 

 and shoot forward. 



The species which, like the collared adder, and the pela- 

 mides, can sustain themselves in the water, swim on the sur- 

 face of this fluid by vertical undulations, and breathe ex- 

 ternally. 



The muscles of the ophidians are endued with a contrac- 

 tile force, which is truly prodigious. The boa constrictor, 

 by entwining itself round them, can suffocate almost the 

 largest quadrupeds between its folds, which may be com- 

 pared to tightened knots. The same is done to the large 

 squirrels of North America, by the coluber constrictor, which, 

 moreover, according to Catesby, runs with the most incon- 

 ceivable agility over the roofs of the houses in Carolina. 

 This muscular power partly explains to us why the ancients, 

 in their mythological traditions, so often founded on exact 

 observations, have made strength the attribute of the ser- 

 pent, and why they supposed that Achelous, about to com- 

 bat with Hercules, clothed himself with the form of this rep- 

 tile. It is also, without doubt, its agility, and the prompti- 

 tude of its movements, which caused it to be selected from 

 the very origin of civilization among the Egyptians and the 

 Greeks as a symbol of the swiftness of time, and the rapidity 

 with which the years roll on in succession, one after another. 

 It was also chosen as the emblem of Saturn, and as that of 

 eternity, without beginning and without end, like the perfect 

 circle formed by this animal in biting its tail. 



The principal pieces of the skeleton of the ophidians, pre- 

 sent modifications not found in the other vertebrated ani- 

 mals. They are destitute, for instance, of sternum and of 

 pelvian bones, not to mention those of the limbs. The spine 

 is composed of vertebras, which have pretty nearly the same 

 form, from the head to the tail. 



Among these vertebrae, the number of which is consider- 



