General forms
Among 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).[1]
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.
Foot
A human foot - Enlarge to view legend
Latin pes
Artery dorsalis pedis, medial plantar, lateral plantar
Nerve medial plantar, lateral plantar, deep fibular, superficial fibular
MeSH Foot
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.
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