4 THE STRUCTURE AND LIFE OF BIRDS chap 



in body and in brain he presents a striking contrast 

 to the bird. But the evidence of anatomy is irresist- 

 ible. From lizard-like ancestors the bird is de- 

 scended. A reptilian fore limb has been modified and 

 adapted for flight, two of the five fingers having 

 disappeared during the process, and one of the re- 

 maining three having shrunk almost to a mere 

 rudiment. The breast bone has attained wonderful 

 dimensions for the attachment of the muscles of 

 flight. The hind leg has been much strengthened so 

 as to make the quadruped a biped and keep the wings 

 from dragging in the mire. The back has been 

 stiffened, since an approach to rigidity is required 

 for flight, and, perhaps still more, for the nearly 

 horizontal carriage of the body in walking. A long 

 neck, snakelike but more supple than a snake, brings 

 the ground within easy reach of the longest-legged of 

 the race. The scales have become feathers. The 

 part of the brain in which the higher faculties reside 

 has grown, so that the forehead rises high. The eye 

 has become large and has acquired a wonderful keen- 

 ness of sight. The three-chambered reptile's heart 

 has become a four-chambered heart, and untold advan- 

 tages have thereby been gained. The lungs have not 

 been enlarged, but their effectiveness has been many 

 times multiplied. In many cases the heavy bones 

 have become hollow and are filled with air. The 

 teeth are gone, but a gizzard or muscular stomach, 

 better placed and equally efficient, has taken over 

 their work. The gastric juices are stronger and equal 

 to dealing with hearty and frequently recurring meals. 

 All this— better heart, better lungs, better digestive 



