FEATHERS. 



423 



The grouping oE the feathers on the anterior hmb and on the 

 tail determines the utility of these organs as wings and steering 

 apparatus respectively. The wing ca,n be folded at two points, 

 viz., at th^ 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, Fig. 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 quills 

 (remiges) are attached 

 along the post-axial bor- 

 der of the fore-arm and 

 manus to the bones of 

 these parts. Those 

 which 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 cubitals (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 poUex. The secondaries vary m 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 wiist) 

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

 cubitalism). The variability of this character extends through 



Fig. 235.— XomenoJature of the plumage and body- 

 regions of Amjielis garrulus (wax-wing). Slightly 

 modified (after Reicheab.ich). Al bastard wing; 

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

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

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

 qtiills ; S forehead ; Sc occiput ; St vent ; T 

 coverts ; W cheek ; Z lore. 



