To make an obviously fictional creature appear realistic, the creator should take into consideration the modifications of almost all of the body's systems as well as its' general ecology. This is what I'm trying to do. In fact, the only bones that I didn't modify for flight from the horse skeleton are the patellas and the cervical (neck) vertebrae. This is the best that I could come up with for a winged horse that can efficiently fly, run and survive. The ability to fly is not to be taken lightly; If their is no need to fly, birds will quickly lose the ability in just a few generations. So I approached this issue with as many refrences as I can. This is what I have: Their skull has only eight true teeth - the incisors. The rest of the teeth have all fused together to form a sort of chopping/grinding block. The eye sockets are larger and the brain case is larger. As is obvious, they have three sets of limbs - two pectoral and one pelvic. The spinal column has a double notch in it to hold two sets of muscles (contrary to popular belief, those funny protrubances on the rib cage do not anchor muscles; they stabilize the thorax in flight). The middle set (the inferior pectoral girdle) is the weakest of the three and is mostly present as a shock absorbent when landing or running. The pelvic girdle holds a lot of power to aid in lift off and running. I chose not to use horse hooves and instead imitated llama feet because landing with hooves = failure. Llama feet grip earth and rock much better and provide better cushioning. Equavis are completely covered in feathers. Their bodies are compact to allow the center of gravity to be under the wings. The lower part of their legs are longer than the upper part - and have much less muscling - to reduce fatigue and to allow the muscles on the upper parts to act as a lever. If you've ever seen a heron, stork, crane, flamingo, et cetera fly, than you may have noticed that they extend their legs out behind them. Equavis do the same. They also, like birds, have less blood vessels in their lower legs. Like birds, equavis have hollow bones and major bones are pneumatic (besides being hollow, these bones are filled with air spaces that are connected to the respiratory system). They also have about nine air sacs that are connected to their lungs spaced through out their bodies. Not only do these make them lighter, it also raises their stamina and extends their breath. I love my Animal Anatomy book and Ornithology book. But I resent not having any colored references. That's all that I can think of for the moment. This is the skeletal design of a species that I will be present in a world that I have created and will hopefully write about.