FEATHERS. 



423 



The grouping ot the feathers on the anterior limb and on the 

 tail deterjnines the utility of these organs as wings and steering 

 apparatus respectively. The wing can be folded at two points, 

 viz., at the elbow joint and the carpal joint ; its surface is 

 formed by the large remiges attached to the forearm and manus, 

 and partly by special folds of skin which stretch between the body 

 and the posterior side of the proximal part of the humerus {post- 

 patagium), and between the upper-arm and fore-arm on the.^pre- 

 axial side {prepatagium, Fis. 234). The prepatagium contains 

 an elastic band which 

 extends along its outer 

 edge from the humerus 

 to the wrist, and which, 

 when the fore-arm is ex- 

 tended, exercises a trac- 

 tion on the thumb side 

 of the carpal joint, and so 

 causes the simultaneous 

 extension of the hand. 



The large wing quilis 

 {remiges) are attached 

 along the post-axial bor- 

 der of the fore -arm and 

 manus to the bones of 

 these parts. Those 

 wliich are attached to 

 the manus are larger than 

 the others and are called 

 primaries or manuals 

 (Fig. 235 HS) ; while 



those which are attached to the fore-arm are called second- 

 aries or cuhitals (Fig. 235 AS). There are usually ten primaries ; 

 of these some are attached to the metacarpals (metacarpal 

 quills), the others to the phalanges of digits 2 and 3 (digitals) ; 

 none are attached to the pollex. The secondaries vary in num- 

 ber (six to thirty or more) ; they are attached to the ulna. It 

 happens in some birds {Anseres, Colymhidae, Psittaci, Accipitres, 

 Columhidae, etc.) that the fifth cubital (counting from the wrist) 

 is absent,there being a gap between the fourth and sixth (aquinto- 

 cubitalism). The variability of this character extends through 



Fia. 235. — Xomenelature of the plumage and body- 

 regions of Ampelis garrulus (wax-wing). Slightly 

 modified (after Reichenbach). Al bastard wing; 

 AS secondaries; B tail-coverts; Ba belly; Br 

 breast ; Hh hind head ; HS primaries • K throat ; 

 N nape ; P scapulars ; R back ; Rt tail with tail- 

 quills ; S forehead ; Sa occiput ; St vent ; T 

 coverts ; W cheeU ; Z lore. 



