THE FROG AND ITS RELATIVES 265 



Representatives: Frogs, tree-frogs, salamanders, toads, newts. 

 Frog. 



External Structure. 



1. Shape, irregular, not graceful. 



2. Covering, loose smooth skin, absorbs water. 



Adapted for protection by color and slime. 

 Adapted for respiration by capillaries, thinness. 



3. Head (no neck). 



Nostrils anterior, connect with mouth, valve. 

 Mouth, large for catching insects. 



Tongue, fixed in front, two tips, sticky. 



Teeth, none below, small on upper jaw and roof. 



Interior structure. 



Nostril openings Eustachian tubes 



Folded tongue, Gullet, trachea. 



Eyes. 



Large, projecting as protective adaptation. 



Can be retracted, three lids. 

 Ears, flat drum on surface of head. 



4. Legs. Anterior, short for support only. 



Posterior, long, strong, for leaping and swimming. 

 Adaptations. 



Powerful calf and thigh muscles. 



Long levers, especially ankle and toes. 



Webbed toes. Large hip bones. 

 Comparison with man (see text). 



Legs homologous to paired fins of fish. 



Legs homologous to legs and arms of man. 



Legs and fins analogous (locomotion). 



Legs and arms not analogous (prehension and locomotion) 



5. Muscles. Spindle shaped as in higher animals. 



Attached to bones with tendons. 

 Not in separate plates like the fish. 

 Internal Structure. 

 Digestion. 



'( tongue, attachment, shape, sticky. 

 Food-getting adaptations -j teeth, upper jaw and roof of mouth. 



I mouth, location, size. 

 Organs of digestion. 



Gullet, short, broad (why?). 

 Stomach, oral, diagonal, covered by liver. 

 Intestine, medium length, coiled (why?), rectum. 

 Glands, salivary and mucous in mouth. 

 Gastric and mucous in stomach. 



f emptying into intestine. 

 Pancreas J 



