14 THE FEATHERED TRIBES. 



tlicy are, in fact, a continuation. Other feathers, attached to the iijipcr part of tlie 

 humerus, lie along the sides of the back, and in many liirds are of great length ; they are 

 called scapularics (No. 5). 



A series of feathers, termed the lesser corerts(No. 6), are disposed in scale-like order, vow 

 after row, ou the fore-arm and carpal joint ; they cover the barrels of the cpiill-feathcrs. Below 

 them extends a series of larger feathers, which sweep across the whig, encroaching far on 

 the primaries, and when the -wing is closed usually hiding the secondaries ; these are the 

 greater eocerts, of which the tertiaries arc a continuation. The mider surface of the wing 

 is lined with softer feathers, termed ^tmler coccrtSi 



The quills of the tail-feathers are hidden beneath what are termed ilte upper fail-coi'crfs 

 (No. 7), which, in some birds, as the peacock, form long, flowing, and exquisitely beautifid 

 plmncs. Beneath the quills of the tail-feathers are covered by wider tail-coverts (No. 8), 

 consisting of lax fcathci's, which in some birds, as the marabou, form extremely soft and 

 deHcate plumes. On the cheek maybe seen a tuft of feathers covering the ears (No. 10), 

 and therefore called ear coverts, and there is onl}' to be added the tail (No. 9) to com- 

 plete a general view of the plumage of birds. 



The ■n"ing is set in motion by powerfid muscles, and becomes au organ fitted for swim- 

 ing, that is to say, for energeticallj^ repelling a fluid much more resisting than the air. 

 Birds whoso wings are changed into fins are called iinpenui (no wings) ; those whose wings, 

 although furnished with feathers, is reduced to a stump, arc called rudipeiiiii (rudimen- 

 tary wing) ; all others organized for flight are called aJipeiiiii. 

 This engranng (fig. 10) exhibits to view the following parts : — 



T, wing coverts ; p B, spurious wing or winglet, composed of the feathers of the 

 thmnb ; R V, quill feathers ; R S, secondaries ; p s, scapularies. 



In birds designed for flight the wings vary in length according to the species ; and 

 besides the differences in the absolute length of the wing, there are others in the relati\'e 

 length of the feathers of the wing. When the longest feathers occupy the edge side of 

 the wing, and then go on decreasing from this edge, the wing is acute, and the bird is 

 called aeufipeniius. 



When, on the contrary, the longest feathers correspond with the middle of the hand, 

 the wing is obtuse, and the bird is called ohfusiprnnus. 



Each of these types inaj' oft'er three cases ; when the second feather of tlie ^\■i^g, begin- 

 ning from the edge, is the longest, the mng is simply acute ; when the first feather is as 

 long or longer than the others, the wing is sur-acufe ; when the third feather is equal to 

 the second, the wing is sub-acute. 



In the same way three degrees have been established iu the obtuse wing ; if it is the 

 fourth feather, which is the longest, it is simply obtuse; if it is the third it is sub-obtuse; 

 if it is the fifth, or following, it is sur-obtuse. 



These characteristics arc of great importance, since they cxpi'ess the degree of the 

 power of flight. The bird with acute wings moves with greater agility than the one 

 whose wings arc obtuse ; the obtuse wing is notliing else tlian an acute wing, the extre- 

 mity of which has undergone an oblique section. And the further the wing, which is the 

 arm of the lever of the power, has its extremity distant from the point of siq3port or centre 

 of movement, the more energetic it is in I'cpclliug tlie air whicli pivsents the resistance. 

 Thus the man(eu\res of tlio bird with acute wings arc more rapid and more varied than 

 ihose of other birds; it can move in all directions, like a boat with oars, and easily seize 

 a prey which is trying to escape with obtuse wings, and which, like a ship with sail, can 

 only tack about. Hence the names saitinij birds, and roaiiKj birds, according as their 

 wings are obtuse or acute. 



As the direction in which a bird <'an fly dcjiends greatly on the form of its wings, 

 (Sir Everard Home justly infers that a motion directly upwards can only be pcrloruied 



