246 CLASS REPTILIA. 



member, the extremity of which even appears in 

 some externally, in the form of a little crook.* 



We subdivide them into two tribes. 



That of the Double Walkers has the lower 

 jaw supported, as in all preceding reptiles, by a tym- 

 panic bone immediately articulated to the cranium — 

 the two branches of this jaw are soldered in front, 

 and those of the upper jaw are fixed to the inter- 

 maxillary bone, which prevents their mouth from 

 dilating as in the following tribe, and makes the 

 head all of a piece with the rest of the body. This 

 form enables them to move either backwards or 

 forwards. The osseous framework of the orbit is 

 incomplete behind, and the eye very small. As for 

 the rest, their body is covered with scales, the anus 

 situated very near its extremity, the trachea long, 

 the heart very far back. None are known to be 

 venomous. 



There are two genera, one of which approximates 

 to the chalcides and bimana, the other to the 

 snakes, and acontias. 



AMPHISB(ENA,t L., 



Have the entire body surrounded by circular ranges 



* See the German dissertation of M. Meyer, on the posterior extremi- 

 ties of the ophidians, in the xiith vol. Curieux de la Nature of Bonn. 



•f- From «/^9if and ^mvhm, walking in both directions. The ancients be- 

 lieved that it had two heads. This name has been erroneously applied to 

 serpents of America, unknown to the ancients. 



