132 



ANIMAL BIOLOGY 



five separate bones in the palm. Do any of the frog's 

 fingers have three joints ? Compare also the leg of man 



and the hind leg 

 of the frog (Figs. 

 25 3 and 399). Does 

 the thigh have one 

 bone in each ? The 

 shank of man has 

 two bones, shin and 

 splint bone. Do 

 you see a groove 

 near the end in the 

 shank bone of a 

 frog (Fig. 252), in- 

 dicating that it 

 was formed by the 



union of a shin and 

 Fir.. 253. -SKELETON OF FROG. spHnt bone ? The 



first two of the five bones of the ankle are elongated, giv- 

 ing the hind leg the appearance of 

 having an extra joint (Fig. 253). The 

 foot consists of six digits, one of which, 

 like the thumb on the fore limb, is 

 rudimentary. The five developed toes 

 give the five digits of -the typical verte- 

 brate foot. Besides the five bones cor- 

 responding to the instep, the toes have 

 two, three, or four bones each. How 

 is the hind foot specialized for swim- 

 ming? Which joint of the leg con- 

 tains most muscle? (Fig. 254.) Find other bones of the 

 frog analogous in position and similar in form to bones in 

 the human skeleton. 



FIG. 254. LEG MUS- 

 CLES OF FROG. 



