STERNA OF WINGED BIRDS. 319 



by the shingly bases of the New Zealand cliffs, are 

 all as much in harmony with the scenes in which we 

 find them, as the parrot is with the perennial bloom 

 of the tropical forest, or the albatross or the petrel is 

 with the expanse of the world of waters. Wings are 

 not wanted upon extended flats of firm surface ; they 

 are for the " ups and downs" of feeding grounds ; 

 and, therefore, those birds to which wings would be an 

 incumbrance have them not, but in their stead organ- 

 isations better suited to their haunts. 



STERNA OF WINGED BIRDS. 



In considering the sterna of birds as indices to 

 their different powers of flight, the elevated crest 

 or keel is certainly the most important ; while of 

 the other bones which form part of the sternal 

 apparatus, the most important is the clavicle, for 

 as we have seen, the coracoid bones are constant, 

 not very much dependent on tlie rate or style of 

 flight, and the scapulars, though of weaker structure, 

 and less fitted for bearing cross strains, are often 

 more developed in birds which fly heavily than in 

 those which fly well. 



But still the form and consistency of the sternal 

 bone itself, independently of its ridge or its appen- 

 dages, vary considerably in birds of different powers 

 of wing. The firmer the sternum is, that is, the more 

 completely that it consists of one plate of bone, with- 

 out apertures, and with the different pieces in which 

 ossification begins in the young birds, united by 

 bone, the bird flies the better and the more power- 

 fully ; and of course, in proportion as the sternum is 

 deficient in those qualities, the flight of the bird is 

 less elevated and less capable of being continued. 

 If the sternum, besides being of solid bone, is of 



