BATRACHIA 



131 



upper and lower eyelids of the same thickness ?■ With 

 which lid does it wink ? Close its eye ? 



Observe the large oval car drum or tympanum. What 

 is its direction from the eye? (Fig. 251.) The mouth? 

 Is there a projecting ear ? Does the frog hear well ? 

 What reason for your answer ? As in the human ear, a 

 tube (the Eustachian tube) leads from the mouth to the 

 inner side of the tympanum. 



How many nostrils? (Fig. 251.) Are they near to- 

 gether or separated ? Large or small ? A bristle passed 

 into the nostril comes into the mouth not far back in the 

 roof. Why must it differ from a fish in this ? 



How do the/ore and hind legs differ ? How many toes 

 on the fore foot or hand ? On the hind foot ? On which 

 foot is one of the toes rudimentary ? Why is the fore limb 

 of no assistance in propelling the body in jumping ? Do 

 the toes turn in or out? (Fig. 250.) How does the frog 

 give direction to the 

 jump ? What would 

 be the disadvantage 

 of always jumping 

 straight forward 

 when fleeing? Which 

 legs are more useful 

 in alighting ? 



Divisions of the 

 Limbs. — Distinguish 

 the upper arm, fore- 

 arm, and hand in the 

 fore limb (Figs. 252 and 253). Compare with skeleton of 

 man (Fig. 399). Do the arms of a man and a frog both 

 have one bone in the upper arm and two in the forearm ? 

 Both have several closely joined bones in the wrist and 



Fig. 252. — Skeleton of Frog. 



