152 CHARACTERS OF VERTEBRATE ANIMALS 



lining of the crop. The helpless nestling is very imperfectly 

 clad with feathers, and these down-feathers are much simpler 

 !n nature than the ordinary feathers of the adult bird. 



CLASSIFICATION OF BIRDS 



Excluding fossil forms, birds are divided into two sub-classes 

 of very unequal size: I. Flying Birds (Carinatae), of which the 

 Pigeon is an example; and II. Running Birds (Ratitse), of which 

 the best-known kind is the Ostrich. 



I. Flying Birds (Carinatee) are more or less perfectly adapted 

 for flight, as will have been seen from the typical example just 

 described. The most striking characters are found in the structure 

 of the wings and the keeled sternum, in reference to which latter 

 feature the group is technically called Carinatae (L. carina, a keel). 



Although the existing species of flying birds are extremely 

 numerous, they agree so closely among one another in most 

 essential features that it is exceedingly difficult to divide them 

 into orders, but eighteen of these are commonly recognized, 

 though the distinctive characters of many of them are founded 

 upon comparatively trivial matters, and we do not get the broad 

 lines of division existing in the case of Mammals. The orders 

 are as follows: — 



I. Perching Birds (Passeres); 2. Picarian Birds (Picariae); 

 3. Owls (Striges); 4. Parrots (Psittaci); 5. Pigeons and Sand- 

 Grouse (Columbae); 6. Gulls (Gaviae); 7. Plovers (Limicolae); 

 8. Bustards and Cranes ( Alectorides) ; 9. Rails (Grallae); 10. 

 Game-Birds (Gallinse); 11. Tinamous (Crypturi); 12. Eagles 

 and Vultures (Accipitres) ; 13. Ducks, Geese, and Flamingoes 

 (Anseres); 14. Herons and Storks (Herodiones); 15. Pelicans 

 and Cormorants (Steganopodes) ; 16. Petrels and Albatrosses 

 (Tubinares); 17. Divers and Grebes (Pygopodes); 18. Penguins 

 (Impennes). 



Order i. — Perching Birds (Passeres). 



This order is regarded as the highest of the sub-divisions of 

 birds, and the large majority of them are included in it, more 

 particularly those which are familiarly known as " song-birds ". 

 The first toe can be moved independently of the others, which 

 is not the case in other birds, and possesses a larger claw than 



