Bird feet and legs

Most birds are digitigrade animals, which means that they walk on their toes, not the entire foot. Some of their lower bones of the foot (distals and most of metatarsals) are fused to form tarsometatarsus – a third segment of the leg, specific to birds. The upper bones of the foot (proximals) in turn are fused with the tibia to form tibiotarsus, as over time the centralia disappeared. The fibula is also reduced.

The legs are attached to a very strong assembly consisting of the pelvic girdle extensively fused with the uniform spinal bone (also specific to birds) called the synsacrum, built from some of the fused bones.

Bird leg and feet anatomy is very diverse. It reveals many accommodations to perform a wide variety of functions.

Birds are generally digitigrade animals (toe - walkers) as reflected in the structure of their leg skeleton. They use only hindlimbs to walk, which is called bipedalism. As mentioned earlier, most bones of the avian foot (except toes) are fused together or with other bones, having over time changed function.

Some lower bones of the foot are fused to form tarsometatarsus – a third segment of the leg specific for birds. It consists of merged distals and metatarsals II, III and IV. Metatarsus I remains separated as a base of the first digit. Tarsometatarsus is the extended foot area giving the leg an extra lever length.

The upper bones of the foot (proximals) are fused with the tibia to form tibiotarsus, while the centralia disappeared. The anterior (frontal) side of the dorsal end of the tibiotarsus (at the knee) contains a protruding enlargement called the cnemial crest.

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Wikipedia