1886.J on the Wings of Birds. 365 



digits appear to correspond with tlie pollex, index, and mediiis of tlie 

 typical pentadactyle manus ; the second is always the longest. Both 

 it and the pollex frequently bear small horny claws at their extremity, 

 concealed among the feathers and functiouless, but very significant 

 in relation to the probable original condition of the avian wing. These 

 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 thii'd 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, &c.), seven to the metacarj)us ; 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 {p'se-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 developed, the distal always rudimentary ; but the 

 former may show every degree of shortening, until it becomes quite 

 rudimentary, or even altogether absent, as in Fringillidse and other 

 " nine-primaried " birds, in which there are six metacarpal remiges, 

 one ad-digital, two mid-digital, and no prsedigitals, 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 together by means of minute hook- 

 lets, and so present a continuous, solid, resisting surface to the air. 



Such is the characteristic structure of the wing in almost all 

 carinate birds, whether powerfully developed for flight, as in the 

 eagles, albatrosses, or swifts, or whether reduced in size and power 

 to practically useless organs, as in the extinct great auk, the dodo 

 and its kindred, weka rail, notornis, cnemiornis, &c., most of 

 which, being inhabitants of islands containing no destructive land 

 mammals, appear to have lost the principal inducement, and with 

 it the power, to fly. 



In the penguins (S;p'heniscomorplise) 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 booklets. They form an imbricated covering of both 

 surfaces of the wing, including the broad patagium which extends from 

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

 the bones, and cannot be divided into distinct groups, corresponding 



