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 
