282 



A'EKTIiUKATK AXIMALS. 



Khaped lioiie, wliich is terliiiically called tlie " fureuluni," but is 

 familiarly called the "iLieny thought." The funrtinu of this cla- 

 vicular arch is to keep the wings asunder during tlieir downward 

 stroke, and the strength of the fiirculuni varies, tlierefore, with the 

 powers of iliglit enjoyed ))y each l.iird. The hones which form the 

 limb prcjpjer, or "wing," are considerably modified to suit the 

 special function of flight, but essentially the same parts are present 

 as in the fore-li]iili of tlie Marnnials. Tlie upper arm (fig. 203) is 

 constituted Ijy a single bone, the Iiiiiiiiriis {//), which is generally 



short and stout. The fore-arm 

 is ciinipo.sed of two bones, the 

 r (dills (/■) and the vlaa (it), of 

 which tlie ulna is the bigger. 

 These .are followed biy the 

 sni.-dl bones, which form the 

 wrist or riii-/)ii.<: (ij), but the.se 

 ;ire reduced to iirn in number. 

 The carpus is followed liy the 

 bi'Ues wliich constitute the root 

 of tlie hand or 'iiirfin-iirpiit: (/«), 

 l.iut these are alsri reduced to 

 iirn, instead of being five in 

 number, as they are in most 

 Mammals. The two metacar- 

 ]i,'il bones are al.'o amalgamated 

 together at both ends, so as to 

 form a single piece, at the b.'ise 

 of wliicli, on its outer side, 

 ii a rudimentary digit, the 

 '■thumb" (7), which carries a 

 tuft of feathers, known as the 

 '•bastard wing." The meta- 

 carpal bones, tinally, su])port 

 eaeh a single finger {j>), of 

 which one is never composed 

 of mole th;in one bone or /i/ni/n n.r, whilst tlie otiier is comjiosed of 

 two or three jihalanges. ('I'o understand thoroughly tile leading 

 3nrjdifi(;;itions i.if the limbs of Dirds, the student will do wi.')! to refer 

 to the general deserijition of the limbs of Vertebrates, p|i. i!2i', 223, 

 tig.s. KiO, KM.) 



As reg.-irds the coni|iosition of the hind-limb in Ilirds, the two 

 halves of the ]iel\ir ;iri-li (■/.<•., the iniioiiiiini/,' lunirx) .always form a 

 single jiii'ce each, and tlie\ are always firmly united A\itli the s.acral 

 region 'if the spine. AVith the single exce|itioii, howe\'er, of the 



;-j, Pllllla 



