SALAMANDER, FROG, AND OTHER AMPHIBIANS. 171 



skull remain cartilaginous as in fishes. Another distin- 

 guishing mark is that the skull is connected with the ver- 

 tebral column by two condyles, these being bony, rounded 

 projections which fit into corresponding sockets in the first 

 neck- vertebra. In having two condyles, Amphibians differ 

 from lizards and birds, and resemble mammals. Another 

 new feature is the presence of short, rudimentary ribs. 

 Eyelids are often present, no fishes having them. Thus, 

 as a rule, Amphibians are characterized by having true leg*, 

 toes, and lungs ; the toes ivithout claws, the skin smooth, 

 without visible scales ; the skull has few investing bones, 

 but with two condyles ; external gills are often present ; 

 there is a sternum and ribs ; the heart is three-chambered, 

 and most of the species undergo a metamorphosis. 



ORDERS OF BATRACHIA (AMPHIBIANS). 



1. Body long, eel like, with gills; no 



hind legs Tmchytomata. Siren. 



2. Body flat, with gills ; four legs Proteida. Mud-puppy. 



8. No gills in adult life Urodela. Salamanders. 



4. Body snake-like; no feet, no tail .... GymnopMona. Blind Snake. 



5. Extinct ; body partially scaly Stegocephtila. Labyrinthodonts. 



6. Tailless, with four legs, long toes; 



great leapers ; young with tails. .Anura. Toads, Frogs. 



The Sirens. These singular creatures are eel-like in their 

 form and movements, with gills on the sides of the head. 

 They have no hind legs, and the small, weak fore legs are 

 three- or four-toed. The great siren (Siren lacertina) is 

 two or three feet in length, and is four-toed. It lives in 

 swamps and bayous in the Southern States, especially in rice 

 lands. Its food is supposed to be earth-worms, insects, 

 etc. 



The Mud-puppy. The Proteida are flat-bodied, with 

 bushy thick gills, of a beautiful deep red beneath, with 

 gill-openings, while the jaws are armed with small conical 

 teeth. 



The Proteus of Austrian caves is blind, having no use 

 for eyes, as it lives in total darkness ; it has three toes in 



