foot, in anatomy

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Foot

foot, in anatomy, terminal part of the land vertebrate leg. The term is also applied to any invertebrate appendage used either for locomotion or attachment, e.g., the legs of insects and crustacea, and the single locomotive appendage of the clam. Among land vertebrates, the foot includes the area from the ankle through the toes. In some animals, including humans, the weight is supported on the entire surface of the foot. Such animals are known as plantigrade. In digitigrade animals, e.g., the dog and cat, the weight is supported on a pad behind the toes, while the ankle and wrist areas remain elevated. Such animals as horses and cows that walk on a naillike structure (hoof) at the end of one or more toes are known as unguligrades. Like the hand, the human foot has five digits. However, it is less flexible and lacks an opposable digit (thumb) for grasping, as do the feet of most primates. The human foot consists of 26 bones, connected by tough bands of ligaments. Seven rounded tarsal bones (the internal, middle, and external cuneiform bones, navicular, cuboid, talus, and calcaneus) lie below the ankle joint and form the instep. Five metatarsal bones form the ball of the foot. There are 14 phalanges in the toes (two in the great toe and three in each of the others). The foot bones form two perpendicular arches that normally meet the ground only at the heel and ball of the foot (see flat foot); these arches are found only in humans. The use of the stride, a form of walking in which one leg falls behind the vertical axis of the backbone, is also a singular aspect of the human foot. The stride is thought to be an evolutionary advance from running, and is related to the unique structure of the human foot.

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