Make a conclusion about the relationship of the external and internal structure of the bird with the way of movement.

The ability to fly in birds is a consequence of changes in the external and internal structure. Flying birds always have a small body weight due to the structure of the bones of the skeleton, which have air cavities in them. The forelimbs of the birds were transformed into wings, the phalanges were greatly lengthened. The bird’s body and wings are covered with feathers. Due to the special structure of the feather, the bird can be held in flight. Feathering also lightens the force of air resistance. Promotes flight and double breathing in birds. Birds breathe on both inhalation and exhalation due to the presence of lung sacs.