THE FROG 175 



the one at the elbow, a hinge joint; and the one at the wrist, 

 a compound joint. Describe the characteristics of each. 



c. In the same way the bones of the hind Hmbs, or pel- 

 vic girdle, may be studied. Find the bones composing the 

 socket in tlie spinal column, the femur with the ball fitting 

 into it ; the double bone, tibia and fibula, united but shown 

 by the grooves ; the tarsus, metatarsus, and phalanges in 

 order similar to those of the fore limbs. Draw. Is the pel- 

 vic girdle an arch? Why do you think so? Draw it and 

 compare with the shoulder girdle. 



Classification. — The position of the frog in the branch of ver- 

 tebrates is given in the study of fishes. It remains to give the class- 

 ification of the class Amphibians. 

 Class Amphibia. 



Body long, eel-like, with persistent gills. 



Hind limbs absent Order Trachystomata (sirens). 



Gills not persistent, gill openings usually absent. 



Tail present, 4 appendages (rarely 2) present. Order Urodela. 

 (Salamanders). 



Body short, larvae tailed, adult tailless, four limbs. Order Anura 

 (Frogs, toads). 

 Families of Anura. 



1. Thoracic region capable of expansion. 



a. Upper jaw toothless, toes webbed — terrestrial. Bufoni- 

 dae (toads). 



b. Upper jaw with teeth, fingers and toes more or less dilated 

 at tips forming disk, order Arboreal. Hyledae (Tree frogs). 



2. Thoracic region incapable of expansion. 



Toes webbed and usually fingers, upper jaw containing teeth, 

 tympanum conspicuous — Family Ranidae (Frogs). 

 Development. — The development of the frog is an easy 

 and interesting subject and should be watched by every stu- 

 dent. In the early spring the eggs may be obtained in 



