OF BIRDS. 
IX 
stronger than the rest ; the hind toe is sometimes wanting. 
This order contains the ostrich family, the bustards and 
plovers ; the cranes, herons, and storks ; and the snipes and 
woodcocks. 
6. Palmipedes, or web-footed birds. These birds have 
the legs and feet short, and placed behind, with their fore 
toes united by a thick and strong membrane. The neck is 
much longer than the legs, and their bodies are covered 
with a dense layer of down, beneath the outer plumage, 
which is close, and imbued with an oily fluid that repels the 
water. The principal birds in this order are the coots and 
grebes, the auks and penguins, the petrels, the pelican and 
cormorant, and the swans, ducks, and geese. 
Not only does the form of the bird fit it for flying, but 
its lungs are extended by means of air-cells extending among 
the muscles; and its bones are hollow, and not filled with 
marrow, but with air. Other circumstances in their internal 
structure serve to facilitate the flight of birds, and to make 
them quite at ease when on the wing. 
In variety birds far exceed quadrupeds. There are many 
thousand species, distinguished from each other by differ- 
