FLYING ANIMALS. 29 



wing, whereas the outer finger is by far the most im- 

 portant element in that of a Pterodactyle. 



It would involve a large amount of detail to give a 

 full description of the arrangement of the feathers of 

 a bird's wing ; and it must accordingly suffice to say, 

 that the large flight-feathers carried by the pinion are 

 known as the primaries, while those attached to the 

 larger bone of the fore-arm are termed secondaries; 

 the smaller feathers which overlie these being desig- 

 nated as the wing-coverts. In all living birds, as we 

 have said, the bones representing the fingers are 

 flattened, and those of the index and third fingers 

 more or less united together. In the Archceopteryx, 

 which is the oldest known bird and a contemporary of 

 the Pterodactyles of the Lithographic Limestones of 

 Bavaria, all the three fingers were, however, perfectly 

 separate from one another, and each ended in a claw ; 

 while the index was not greatly larger than the other 

 two. We have, therefore, in this bird a decided 

 approach to reptiles ; from which class it is considered 

 that birds were originally derived. 



In addition to their wjigs we must not omit to 

 mention that the tails of birds form an important aid 

 in flight, when they act as a kind of rudder. In all 

 living birds the bones of the tail are extremely few in 

 number, and all the large tail-feathers take origin close 

 together, and are generally spread out in a more or 

 less fan-like manner. Our old friend the Archseopteryx 

 had, however, a very long lizard-like tail, with a pair 

 of feathers arising from each of its numerous joints, 



