Bird Anatomy

Wings

Skeleton 
All birds have the same basic plan, though different life styles have meant that they have evolved different variations on the central theme. Birds such as swans have more vertebrae in their necks than those like parrots who have very short necks. Swans have 25 vertebrae, parrots have 9. Necks are useful for getting your mouth to places you do not really want to take your whole body, like the bottom of a pond. They are also useful for turning your head, when your eyes are fixed deep in sockets, without having to turn your whole body. Most flightless birds, having no need of the large flight muscles, have therefore, no need of the large keel or sternum that flying birds have. The exception to this rule are penguins who effectively fly through the water with their modified wings and still need large muscles to power them.

Bird's inherited their basic skeleton from their reptilian ancestors. The constraints of flight however have meant that birds have had to modify it in several major ways. Flight means lifting the birds weight, so the first major consideration is reduction in weight. The lighter you are the easier it is to fly. The main ways birds have lost weight is through the loss of teeth and the large jaw bones needed to support teeth, the loss of nearly all the tail and reduction of the skull. Though a bird's major limb bones are hollow with internal struts for support, this makes them stronger not lighter; a bird's leg bones for example are often heavier than those of similar sized mammal or reptile.

http://www.life.illinois.edu/ib/461/External_Anatomy.pdf