Birds and Birding's Guide to:

Watching THE ANATOMY OF BIRDS

Bird Leg Bones

The uppermost bone of the leg, the femur, is always short, even in wading birds, and usually pneumatic, or permeated by air. The extreme of shortness and width is found in the extinct diving bird Hesperornis, in which the femur suggests that of a seal.

The knee-pan, or patella, is usually small, except in such swimming birds as Cormorants and the extinct Hesperornis, where the head of the tibia is short, and it is largely developed to serve for the attachment of muscles. In Grebes and Loons the upper end of the tibia is greatly extended and the knee-pan correspondingly reduced, appearing as a small splint of bone back of the process.

The tibia is much the larger bone of the lower leg, the fibula being flat and splintlike in character, never quite reaching the lower end of the tibia and commonly not extending more than two thirds of its length. The length of the tibia is related to a bird's habits, being longest in wading birds, coming next in runners, and of considerable development in swimming birds.

The foot of a bird never contains more than four toes, and there may be but two, as in the Ostrich, while the three principal metatarsal bones are united into one, with which the second row of tarsal bones is fused, this forming the tarsometatarsus, or, as it is commonly called, tarsus. The bones corresponding to our heel bone, calca-neum, and its neighbor, astragalus, unite with the tibia, so that the ankle joint of a bird, like that of reptiles, is between the bones of the ankle, and not as in mammals between the leg and ankle.

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