OPHIDIA. 45 



regular form of the body it moves backward or 

 forward with equal facility ; and, as the tail is blunt 

 and almost as thick as the head, and the eyes so 

 small as to be scarcely observable, it is not easy 

 at first to determine the one from the other. The 

 Ampliisbcence are not venomous ; the body is sur- 

 rounded with rings of square scales ; the jaws are 

 still so constructed as to be incapable of stretching 

 in the manner of the true Serpents. They have 

 but one lung. 



In the true Serpents, which are very numerous, 

 the jaws are so loosely jointed with each other as 

 to be capable of a very wide separation, enabling 

 them to swallow animals larger than their own usual 

 bulk. The palate is armed with sharp teeth, which 

 curve backward, and aid in the swallowing of the 

 prey. Most of them have but one large lung. Their 

 motion is peculiar ; the ribs are very numerous, and 

 serve as feet ; the animal resting on their extremi- 

 ties and moving them in turn, just as a Centipede 

 crawls, whose feet indeed they exactly resemble, 

 except in being within the skin. At the same time, 

 it is upon the lateral motion of the body, and the al- 

 ternate lateral pressure of successive portions of it, 

 that the Serpents mainly depend for the rapidity of 

 their progression.* 



The Serpents are conveniently divided into those 



which are harmless and those which are venomous. 



The differences between these are not sufficiently 



obvious to be manifest at a glance ; but they can 



* Bell's Br. Rep. 



