GENERAL LIFE. 621 



Brigade II. 



3. Legion Alectomorphce. 



8. Tinamiformes, tinamou. 



9. Galliformes, e.g., fowl, pheasants, Ofisthocoiims. 



10. Gruiformes, e.g., cranes, rails, bustards, 



11. Charadriiformes, e.g., plovers, gulls, sand grouse, pigeons. 



4. Legion CoracomorphEe. 



12. Cuculiformes, e.g., cuckoos, parrots. 



13. Coracioformes, e.g., rollers, owls, woodpeckers. 



14. Passeriformes, e.g., crows, birds of paradise, finches, 



thrushes, swallows, &c. &c., in fact more than half the 

 known birds. 



GENERAL LIFE. 



Flight. — As birds are characteristically flying animals, 

 many of their peculiarities may be interpreted in adaptation 

 to this mode of motion. 



(a) Shape and General Structure of the Body. — The 

 resistance offered by the air to the passage of a body through 

 it depends in part on the shape of the body, and the boat- 

 like shape of the bird is such that it offers relatively little 

 resistance. The attachment of the wings high up on the 

 thorax, the high position of such light organs as lungs and 

 air sacs, the low position of the heavy muscles and digestive 

 organs, the consequently low centre of gravity, are also 

 structural facts of some importance. It must be remem- 

 bered, however, that the frictional resistance of the air is 

 slight. 



\b) The Muscles of Flight. — The most important is that 

 which covers the whole of the breast bone, the pectoralis 

 major. It brings the wing downward, forward, and back- 

 ward, keeping the bird up and carrying it forward. As it 

 has most work to do, it is by far the largest. Internal to it 

 lies a second muscle, the pectoralis minor, which raises the 

 wing for the next stroke. Besides these two great muscles, 

 there are others of minor importance, the deltoides externus 

 and three coraco-brachials, all of which help to raise the 

 wing. On an average these muscles of flight weigh about 

 one-sixth of the whole bird, but the proportion is often 

 much greater, amounting to nearly one-half in some pigeons. 

 Buffon noted that eagles disappeared from sight in about 

 three minutes, and a common rate of flight is about fifty 

 feet per second. 



