Skeletonderdelen van zeevogels (3): Vleugels

Bird wings are actually modified fore limbs and show many structural similarities to the fore limbs of other vertebrates. Bird wings, however, have a different function: flying, sometimes combined with underwater propulsion. Different ‘flight styles’ determine the shape and relative size of the wing bones. The seabird wing consists of eleven bones, sometimes ten or twelve: the humerus, ulna and radius forming the upper arm. Shearwaters, gadfly petrels, albatrosses and some other petrels possess a small sesamoid bone in the pit of the elbow, which operates as a supporting strut of the patagial fan. Two carpals, one carpometacarpus and three digits of which the largest consists of two phalanges form the hand part. In wing propelling divers the humerus is relative short and flattened for streamline and more strength to cope with the strong forces needed for propulsion in a high-density medium like water. In gliders like albatrosses and large petrels the humerus is rounded and relatively long to very long. The hand part differs very much compared with mammals and reptiles. It consists of a reduced set of carpals. Metacarpals and fingers: a free moving thumb or alula, a long second finger that holds the last large primary and a rudimentary and embedded third finger