Toe

Toes are the digits located at the end of a tetrapod's foot. They serve vital roles in movement, balance, and weight-bearing for many different animals. The way an animal moves affects how its toes interact with the ground. For example, cats are described as digitigrade because they walk on their toes. Humans and other animals are plantigrade, meaning they walk on the soles of their feet. There are also unguligrade animals, which walk on hooves located at the very tips of their toes.

Inside the human toe, the structure is made of specific bones called phalanges. Most toes consist of three phalanx bones: the proximal, middle, and distal bones. The hallux, or big toe, is an exception to this rule. The hallux only contains two phalanx bones, which are the proximal and distal ones. A minority of people may also lack a middle bone in their little toe. These bones connect at joints known as interphalangeal joints. Additionally, the proximal phalanx of each toe connects to the metatarsal bone of the foot at the metatarsophalangeal joint.

Movement in the toes is driven by muscles and tendons. Most toe movement involves flexion, which is moving toward the sole, and extension, which is moving toward the back of the foot. For the four smaller toes, the flexor digitorum brevis and extensor digitorum brevis muscles govern this action. Because these muscles attach to the sides of the bones, it is impossible to move individual toes independently. However, the hallux and the little toe have unique muscle sets. The hallux is primarily moved by the flexor hallucis longus and the flexor hallucis brevis. The little toe is controlled by the flexor and abductor digiti minimi.

Sensation and blood supply are also carefully organized in the toes. Blood reaches the toes through the digital branches of the plantar metatarsal arteries. The blood then drains into the dorsal venous arch of the foot. Sensation to the skin is provided by five different nerves. The superficial fibular nerve supplies the top of the toes, except for the area between the hallux and the second toe. The deep fibular nerve supplies that specific gap. The sural nerve provides sensation to the outer surface of the fifth toe. On the bottom, the medial plantar nerve serves the hallux and the inner three-and-a-half toes. The lateral plantar nerve covers the little toe and half of the fourth toe.

There is significant natural variation in how toes appear among humans. Most people have five toes on each foot, but some are born with more. This condition is known as polydactyly.

Other variations include syndactyly or arachnodactyly. Toe length also varies due to genetics. In most humans, the hallux is longer than the second toe. However, a dominant gene can cause a longer second toe, a trait called Morton's toe or Greek foot. Some people may also have a short hallux that turns inward due to the rare genetic disease fibrodysplasia ossificans progressiva. Research by the U.S. Army has even shown that toe shape and breadth can correlate with ethnicity.

Because toes are essential for walking, they are susceptible to various clinical issues. A common injury is a stubbed toe, which is a sprain or strain of the interphalangeal joints. Another injury, called turf toe, occurs when the toe is strained where it joins the foot. Improperly sized shoes can lead to misalignment or orthopedic problems. Some people suffer from Morton's neuroma, which causes pain and numbness between the third and fourth toes. The big toe is also a frequent site for ingrown nails and gout attacks. Deformities like hammer toe, trigger toe, or claw toe can also occur. These can be caused by dislocations or conditions like diabetes mellitus and rheumatoid arthritis.

The history of the word "toe" reveals much about language evolution. The Old English term was "tā," which is a contraction of "tō." This word comes from Proto-Germanic roots and may have originally referred to fingers as well. Many Indo-European languages use a single word to describe both fingers and toes. In classical Latin, specific terms like "pollex" were used for the thumb. The modern term for the big toe is actually a blend of older Latin forms. From an evolutionary perspective, scientists like Haeckel have traced the five-toed pattern from fish fins through amphibian ancestors.