Chap, x.] FLYING ORGANS. 383 



at their base. In the Cetacea all the bones of the 

 fore limb are united in a common integument, and 

 form the " flipper." 



Some forms escape with rapidity by making 

 bounds or jumps ; of these we have examples in the 

 frog, the kangaroo, or the Cape jumping-hare, in all of 

 which the hind limbs are much stronger and longer 

 than the fore limbs. 



Creeping or crawling is best seen in the snakes, 

 which move along the ground by the backward and 

 forward movement of their ribs, which they use as 

 stilts. 



Flying organs are found among fishes in Exoccetus, 

 where the pectoral fins are so greatly elongated as in 

 some species to reach as far back as the caudal fin ; 

 the fins are not actively moved, and seem to have no 

 power of turning the fish to the right hand or the 

 left ; they cannot fly far at a time. 



Similarly modified pectorals are found in Dactyl- 

 op terus. 



Among recent Reptiles, Draco volans, the dragon, 

 or flying lizard, is capable of short movements through 

 the air, owing to the prolongation of some of its ribs, 

 which, when covered with the skin, form a semi- 

 circular wing on either side of the body. The extinct 

 Pterosaurians (Pterodactyle) had the outer digit of 

 the manus as long or longer than the rest of the fore 

 limb ; and there is evidence that, as in the bats, the 

 integument was produced on either side into a mem- 

 brane, the outer edge of which was attached to this 

 digit, and so formed an expansion, by means of which 

 the creature was enabled to support itself in the air. 



Among Mammals the organs of flight are best 

 developed in the Chiroptera (bats) (Fig. 163), where 

 they are formed by the modification of the skeleton, 

 and especially of the fore-arm (see Fig. 149), and by 

 the extension of the integument into the so-called 



