AMPHIBIANS 



253 



Salamander. They are very intimately united into a forked 

 bone, of which the forwardly-directed prongs are the ilia. The 

 bones of the free limb are longer in proportion than in the 

 fore-limb, and the bones of the lower leg, tibia and fibula, are 

 fused together just like the radius and ulna in the fore -limb. 

 Great specialization has taken place in the tarsus, for while 

 that part of it next the fused tibia and fibula is represented by 

 two elongated bones ( = tibiale and fibulare) the rest has dwindled 



CEREBELLUM 



NUS VENOSUS 



PANCBEAS - ^BILE DUCT 



Fig. 157. — General Structure of Frog 



away to insignificant vestiges. All this is to fit the limb for 

 its use as a leaping organ, and changes of similar kind are seen 

 in certain .Mammals which use the hind-limbs in the same way. 

 It is another illustration of the close connection which exists 

 between form and function, though much space would be required 

 to work it out in detail, even had we all the necessary data, which 

 does not appear to be the case. 



Broadly speaking, the digestive organs (fig. 157) agree with 

 those of the Salamander except as regards the teeth and tongue. 

 The teeth are entirely absent from the lower jaw, though they 

 fringe the upper jaw, and occur in two small groups on the roof 

 of the mouth. The long forked tongue has the remarkable 

 peculiarity of being attached to the front of the mouth-floor, 

 with its tip pointing backwards when not in use. It is an 

 insect-catching organ of no mean order of perfection, which can 

 be whipped out of the mouth with great rapidity and as rapidly 

 drawn back, generally carrying with it the desired booty. 



The circulatory organs are built on the same type as those 

 of the Salamander (see p. 240), and keep the impure and pure 

 blood separate to the same extent, supplying the former to lungs 



