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Foot
The foot is a biological structure found in many animals that is used for locomotion. In many animals, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws or nails. more...
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General forms
In land animals, some arthropods and all vertebrates have complex foot organs. The arthropod foot is known as a tarsus, and is distal to the tibia. In primitive insects, the tarsus was a single segment, but in more highly evolved insects the tarsus is composed of up to five segments, generally bearing claws as well.
The feet of terrestrial vertebrates, called tetrapods, first evolved in amphibians from the fins of their aquatic ancestors, fish that ventured out of the water as early as 370 million years ago, in the Upper Devonian Period, perhaps to avoid predation and exploit the greater resource availability on land. The fore- and hindlimbs of these earliest tetrapods evolved from the pectoral and pelvic fins of their fish ancestors, but early forms of feet such as those of Ichthyostega already contained the basic shape of the foot still possessed by tetrapods (although early tetrapods often had more than five digits, the most common form of foot in extant tetrapods).
The feet of terrestrial vertebrates are characterized as plantigrade, digitigrade, or unguligrade. In plantigrade animals, such as frogs, bears, and humans, the bottom of the entire foot supports the weight of the animal. In digitigrade animals, such as wolves and birds, the toes bear the animal's weight, while the upper regions of the foot, the ankle and wrist, remain elevated. Finally, in unguligrade animals, such as cows or horses, even the toes are elevated, the animal standing only atop its nails, which have evolved to bear weight and are called hooves.
The human foot is of the plantigrade form. The bottom of the foot is called the sole and the area just behind the toes is called the ball. The skin at the sole of the foot is denser than any other skin on the human body. The evolution of man has seen the density of the sole of the foot increase as man developed the ability to walk using the legs only.
Bones
The major bones in the human foot are:
Phalanges: The bones in the toes are called phalanges.;
Metatarsals: The bones in the middle of the foot are called metatarsal bones.;
Cuneiforms: There are three bones in the middle of the foot, towards the centre of the body, called cuneiforms.;
Cuboid: The bone sitting adjacent to the cuneiforms on the outside of the foot is called the cuboid.;
Navicular: This bone sits behind the cuneiforms.;
Talus: Also called the ankle bone, the talus sits directly behind the navicular.;
Calcaneus: Also called the heel bone, the calcaneus sits under the talus and behind the cuboid.;
Read more at Wikipedia.org
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