Arrangement and Structure of Typical Feather 

The bird is often describe as a feathered biped. Feathers are supposed to be modified reptilian scales.
The arrangement or distribution of featheres on the body is known as pteylosis. in Ratitae(flightless birds) feathers are uniformaly distributed over the body. But in carinatae (flightlers) feathers are distributed in distinct patches or tracts, called pterylae, which remain separated by featherless inter, called interspaces, called apteria.