Birds Skeleton - Page 2

A Lightweight Skeleton

Although a present-day bird has fewer bones than its ancestors, its skeleton is strong enough for flight due to fusion of many of its bones. Forming rigid girders and platforms, fusion together for rigidity, and others are not, allowing for mobility. Vertebrae in the lower back are joined, as are the bones of the hip girdle, forming a light but strong plate that rests on the thigh bones and supports the bird when it is on the ground. Overlapping projections (similar to cartilage) near the backbone, called the uncinate processes, add strength to the rib cage. Formed by fusion of the collarbones at their base, the wishbone offers structural support for the wings. In flying birds the breast bone is fused to a deep keel (a longitudinal ridge of bone) that provides an anchor for the powerful flight muscles. Generally, the deeper the keel the more powerful the flight.

In contrast to the rigidity of a bird's skeleton, the neck is extremely mobile. This allows the bird to see danger from any direction, catch prey, and preen its feathers, Flexibility is increased by the large number of neck vertebrae, which range from about from 11 to 25. In comparison, mammals -- even the giraffe -- have only 7 vertebrae.