THE WINGS OF BIRDS. 241 



claws are altogether distinct from the large, and often functional, spurs 

 developed in many species from the edge of the metacarpal bones, 

 resembling both in use and situation the corresponding weapons in the 

 hind-feet. The third digit does not bear a second phalanx or claw in 

 any existing bird. 



The quills, remiges, or flight-feathers attached to the bones of the 

 manus (called " primaries "), never exceed twelve in number, and are 

 (as has been recently shown by Mr. Wray) in the very great majority 

 of birds distributed as follows : Six, or in some few cases (flamingo, 

 storks, grebes, etc.) seven, to the metacarpus ; of the remainder or 

 digital feathers, one {ad-digital) is attached close to the metacarpo- 

 phalangeal articulation, and rests on the phalanx of the third digit ; 

 two (mid-digital) have their bases attached to the broad dorsal surface 

 of the basal phalanx of the second digit, which is grooved to receive 

 them ; the remainder (prce-digital) are attached to the second phalanx 

 of the same digit. These last vary greatly in development ; in fact, 

 their variations constitute the most important structural differences of 

 the wing. In most birds there are two : the proximal one well devel- 

 oped, the distal always rudimentary ; but the former may show every 

 degree of shortening, until it becomes quite rudimentary, or even alto- 

 gether absent, as in Fringillidm and other " nine-primaried " birds, in 

 which there are six metacarpal remiges, one ad-digital, two mid-digital, 

 and no prredigitals, or only a very rudimentary one. The smaller 

 feathers at the base of the quills, called upper and under coverts, have 

 an equally regular arrangement. The webs or vanes of all the flight- 

 feathers are made up of a series of parallel "barbs" which cohere to- 

 gether by means of minute hooklets, and so present a continuous, solid, 

 resisting surface to the air. 



Such is the characteristic structure of the wing in almost all cari- 

 nate birds, whether powerfully developed for flight, as in the eagles, 

 albatrosses, or swifts, or whether reduced in size and power to prac- 

 tically useless organs, as in the extinct great auk, the dodo and its 

 kindred, weka rail, notornis, cnemiornis, etc., most of which, being in- 

 habitants of islands containing no destructive land mammals, appear to 

 have lost the principal inducement, and with it the power, to fly. 



In the penguins (Speniscomorphoi) the feathery covering of the 

 wing entirely departs from the normal type. Each feather is like a 

 flattened scale frayed out at the edges, the barbs are non-coherent and 

 have no hooklets. They form an imbricated covering of both surfaces 

 of the wing, including the broad patagium which extends from the cu- 

 bital side of the limb, but appear to have no definite relation to the 

 bones, and can not be divided into distinct groups, corresponding to 

 those described above. The structure of the wing separates the pen- 

 guins sharply from all the other carinate birds. 



The Hatitce, or birds without keel to the sternum, form another 

 very distinct group, distinguished by the rudimentary or imperfect 

 vol. xxx. — 16 



