134 GENERAL ORNITHOLOGY part ii 



as sometimes, though rarely, occurs [chiefly with certain birds of 

 prey and snipe-like birds], the young of both sexes in their first 

 plumage resemble the adult male. 3. When the adult male 

 resembles the adult female, the young of both sexes have a peculiar 

 first plumage of their own, as with the robin [usual]. 4. When the 

 adult male resembles the adult female, the young of both sexes in 

 their first plumage resemble the adults [unusual]. 5. When the 

 adults of both sexes have a distinct winter and summer plumage, 

 whether or not the male differs from the female, the young resemble 

 the adults of both sexes in their winter dress, or much more rarely 

 in their summer dress, or they resemble the females alone. Or the 

 young may have an intermediate character; or again, they may 

 differ greatly from the adults in both their seasonal plumages. 6. 

 In some few cases the young in their first plumage differ from each 

 other according to sex ; the young males resembling more or less 

 closely the adult males, and the young females more or less closely 

 the adult females."— (Z'^'.sc. of Man, ed. 1881, p. 466.) 



h. The Topography of Birds. 



The Contoup of a Bird with the feathers on is spindle-shaped 

 or fusiform (Lat. fnnKs, a spindle), tapering at both ends ; it 

 represents two cones joined base to base at the middle or greatest 

 girth of the body, tapering in front to the tip of the bill, behind to 

 the end of the tail. The obvious design is easiest cleavage of air 

 in front, and least drag or wash behind, in the act of flying. This 

 shape is largely produced by the lay of the plumage ; a naked bird 

 presents several prominences and depressions, this irregular contour 

 being reducible, in general terms, to two spindles or double cones. 

 The head tapers to a point in front, at the tip of the bill, and 

 contracts behind, toward the middle of the neck, in consequence of 

 diminution in bulk of the muscles by which it is slung on the neck; 

 which last is somewhat contracted or hour-glass-shaped near the 

 middle, swelling where it is slung to the body. The body is largest 

 in front and tapers to the tail. The 



Centre of Gravity is admirably preserved beneath the centre 

 of the body, and opposite the points where it is supported by the 

 wings. The enormous breast - muscles of a bird are among its 

 heaviest parts, sometimes weighing, to speak roundly, as much as 

 one-sixth of the whole bird. Now these are they that effect all the 

 movements of the wings at the shoulder- joints, lifting as well as 

 lowering the wings. Did these pectoral muscles pull straight, the 

 lifters of the wing would have to be above the shoulder-joint ; but 

 they all lie below it, and the lifters accomplish their office by 

 running through pulleys to change the line of their traction. They 



