CHAP, xiii BACKBONED ANIMALS 



287 



In many other ways they rank high, for whether we 

 consider the muscles which move the wings in flight, the 

 skeleton which so marvellously combines strength with 

 lightness, the breathing powers perfected and economised 

 by a set of balloons around the lungs, or the heart which 

 drives and receives the warm blood, we recognise that 

 birds share with mammals the position of the highest 

 animals. And while it is true that the brains of birds 

 are not wrinkled with thought like those of mammals, 



FIG. 92. THE COLLOCALIA, WHICH FROM THE SECRETED JUICE OF ITS 

 SALIVARY GLANDS BUILDS THE EDIBLE-BIRD'S-NEST. 



(Adapted from Brehm.) 



and that the connection between mother and unborn 

 young characteristic of most mammals is absent in birds, 

 it may be urged by those who know their joyousness that 

 birds feel more if they think less, while the patience and 

 solicitude connected with nest-making and brooding 

 testify to the strength of their parental love. Usually 

 living in varied and beautiful surroundings, birds have 

 keen eyes and sharp ears, tutored to a sense of beauty, 

 as we may surely conclude from their cradles and love 



