Coloured scanning electron micrograph (SEM) Pneumatic bird bone. The pelican ulna bone is an example of 'pneumatic bird bone' which has numerous spaces with intersecting columns (called trabeculae). Pneumatic bone is a hollow type of bone that contains supporting trabeculae. This type of bone is filled with air and often connected to the respiratory system. Large, soaring birds have developed some pneumatic bones, such as, pelvic girdle, some ribs, humerus, ulna and the femur. The spaces and trabeculae in pneumatic bird bones provide a combination of lightweight and strength as an adaptation to flying. Small birds and diving birds have pneumatic bones. Bird bones contain more calcium than mammalian bones. Magnification: x13 when shortest axis printed at 25 millimetres.
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