236 ANATOMY OF VERTEBRATES. 



from the phalanx representing tlie index, form what is termed the 

 bastard wing {cilida spuria). Those forming what is called the 

 * tail ' of the bird, and supported by the coccyx, are the ^ rectrices,^ 

 or steering quills. The overlying feathers are the ' tail-coverts ' 

 {cahjpteria) ; these bear the ornamental ' eyes' and are so developed 

 in the Peacock as to form what is called the ^ tail ' or * train ' of 

 that gorgeous bird. 



In considering the structures which determine the powers of 

 flight in different Birds, it is necessary to take into account the 

 texture, forms, and proportions of the wing-feathers, as well as 

 the developement of the bones and muscles which support and 

 move them; as much depends upon the mechanical advantages 

 resulting from the shape of the expanded wing. When the 

 primary quill-feathers gradually increase in length as they are 

 situated nearer the extremity of the pinion, they give rise to the 

 acuminated form of wing, as in the Swifts and Humming-Birds, in 

 which the first primary is the longest ; and in the true Falcons, 

 in which the second primary is the longest. In the Hawks the 

 wing is of a less advantageous form, in consequence of the fourth 

 primary being the longest. When the primaries gradually decrease 

 in length towards the end of the pinion, they give rise to a short 

 rounded form of mng, such as characterises the Gallinaceous Order; 

 in which, although the pectoral muscles are immensely developed 

 in order to counteract the disadvantage resulting from the dispo- 

 sition of the primaries, yet they are only able, in consequence of 

 the form of the wing, to carry the bird rapidly forward for a com- 

 paratively short distance, and that mth an exertion and vibratory 

 noise well known to every sportsman. 



The texture of the quill-feathers has also a material effect on 

 the powers of flight. In the Falcons each primary quill-feather is 

 elongated, narrow, and gradually tapers to a point ; the webs are 

 entire, and the barbs closely and firmly connected together.^ In 

 the Owls the plumage is loose and soft, filaments from the barbules 

 extend upon the outer surface of the vane, and one edge of the 

 primaries is serrated ; so that, while they are debarred from 

 so swift a flight as the Hawk, they are enabled, by the same 

 mechanism, to mng their way without noise, and steal unheard 

 upon their prey. 



§ 166. Developement of Feathers. — The first covering of the bird 



' Of so much consequence are the quill-feathers to the Falcons, that when any of 

 them are broken the flight is injured and the falconers find It necessary to repair 

 them ; for this purpose they are always provided with perfect pinion and tail fea- 

 thers regularly numbered. 



