202 ANIMAL ACTIVITIES. 
there is very little attention given to the young of animals 
lower in the scale of life than birds. Here maternal 
and paternal duties seem of the greatest importance. 
Discovery. The senses of birds are very keen, 
especially those of sight and hearing. There is an 
external opening to the 
ear surrounded by regu- 
larly arranged feathers. 
The nervous system re- 
sembles that of the fish 
and frog, but the brain 
is much larger in com- 
parison with the size of 
the body, the cerebrum 
and cerebellum being 
greatly developed. 
Motion. In this func- 
tion birds surpass all 
other animals. Not 
only can some _ birds 
move through the air 
more rapidly than the 
fastest express train, but 
others can swim most 
skilfully in the water, 
and still others are able 
to run faster than a race- 
horse on land. Of 
course, no one bird can do all these things, for when 
wings are greatly developed for very rapid flight, as in 
the swallow, feet are weak and almost useless; and 
when running is specialized, as in the ostrich, wings 
become small and of little use. The swallow does not 
alight even for the purpose of feeding her young. 
In the wing, as we have seen, the bones resemble 
those in the human arm (Fig. 160). At the elbow 
the arm is bent, and the space between the arm and 
forearm is filled with a strong web bearing feathers and 
Fic. 158.—The Skeleton of a Bird. 
