hind limb of birds - Hind Limb of birds; hind limb of birds - At first sight there appears to be a considerable difference between the fore limb and the hind limb. In both there is a long proximal bone, called humerus in the one case and femur in the other, followed by a pair of bones - the tibia and fibula - corresponding to the radius and ulna of the fore limb. But in the hind limb (fig), the foot proper, consisting of metatarsals and phalanges, appears to come immediately after the tibia and fibula. In a sufficiently young bird, what is the apparent lower end of the tibia, and what is equally apparently the upper end of the metatarsus, are detachable; these two halves which are thus detachable are the tarsus, which is the equivalent of the carpus of the wing. The lower bone of the leg is on this account usually spoken of as the tarso-metatarsus. The lower part of this bone is made up of three fused elements, the separation of which from each other is clearly apparent at the lower end of the bone, where the phalanges are attached. In the Penguins the three bones are separated by grooves of a very marked character throughout. In some birds there is a fourth toe, the hallux; in these cases there is a small separate metatarsal loosely fixed to the lower end of the large conjoint metatarsals.