Bird feet and legs only a small extension of the cnemial crest. In grebes both a normal patella and an extension of the cnemial crest are found. The fibula is reduced and adheres extensively to the tibia, usually reaching two-thirds of its length. Only penguins have full-length fibulae. The bird knee joint between the femur and tibia (or rather tibiotarsus) points forwards, but is hidden within the feathers. The backward-pointing "heel" (ankle) that is easily visible is a joint between the tibiotarsus and tarsometatarsus. The joint inside the tarsus occurs also in some reptiles. It is worth noting here that the name "thick knee"
Femur neck usually undergo any change, even in old age; it varies considerably in different persons of the same age. Coxa vara is a deformity of the hip, whereby the angle between the head and the shaft of the femur is reduced to less than 120 degrees. Its opposite is coxa valga. In the female, in consequence of the increased width of the pelvis, the neck of the femur forms more nearly a right angle with the body than it does in the male. It is smaller in short than in long bones, and when the pelvis is wide. In addition to