Digit (anatomy)

Fingers and toes are parts of your limbs.

Most people have five on each hand and foot. Each one has small bones inside. They also have soft skin around them. Some people have extra fingers or toes.

One man named Mikhail Tal had only three fingers on his right hand. Long ago, some fish had bones in their fins. These bones were like early fingers. This helped them change over time. Our hands and feet started from those fish fins.

A digit is a part at the end of a limb. We call them fingers or toes.

Most humans have five digits on each hand and foot. Inside each digit are small bones called phalanges. Soft tissue covers these bones. Human fingers also have a nail at the very end.

Sometimes people are born with extra digits. This is called polydactyly. Some people have fewer digits than normal. One famous chess player, Mikhail Tal, had only three fingers on his right hand.

Digits changed over a very long time. Long ago, fish had fins. Some fish, like Panderichthys, had bones in their fins. These bones were like early fingers.

Over time, these bones changed into the digits we see today. Birds and some dinosaurs also have digits. Birds have three digits in their wings. These grew from an older hand with five digits.

A digit is a part at the end of a limb. We call them fingers or toes.

Most humans have five digits on each hand and foot. Each digit is made of bones called phalanges. Soft tissue covers these bones to protect them. Human fingers also have a nail at the very end.

Some people are born with extra digits. This is called polydactyly. Other people may have fewer digits than normal. One famous chess player, Mikhail Tal, had only three fingers on his right hand.

Your brain has a special map for your digits. This map is in a part of the brain called the somatosensory cortex. This area shows a reflection of your actual fingers. If fingers are fused together, the brain map also looks fused. This is seen in a condition called syndactyly.

Doctors can sometimes use surgery to fix this. At a New York institute, surgeons helped a man named O. G. They used MRI brain scans to check his progress. Before surgery, his brain maps for his fingers were fused. After the surgery, the maps separated into a normal layout.

Digits changed a lot over millions of years. Scientists study how fins turned into limbs. One idea is that digits are unique to tetrapods. Tetrapods are animals with four limbs. Another idea is that early fish already had the start of digits.

A fish named Panderichthys lived during the Devonian period. It lived about 385 million years ago. For a long time, people thought its fins had only one large plate. A 2008 study by Boisvert and others changed this view. They found the fin had at least four fin radials. These bones are similar to very simple fingers.

Other ancient creatures also show how digits might have grown. A creature called Tiktaalik lived in the Devonian period too. It is often called a missing link between fish and tetrapods. Tiktaalik had rows of digit-like bones in its fins. Another fish named Elpistostege also had a very special hand. Its hand had 19 fin radials arranged in blocks. These blocks were up to four radials long. These structures are very similar to the digits we see today.

Birds and dinosaurs also have digits on their limbs. Most birds have only three digits on their hands. These digits are part of their wings. Scientists think these came from the second, third, and fourth digits of an older hand. Some dinosaurs, called theropods, had the first, second, and third digits. A fossil named Limusaurus was found in the Junggar Basin in China. It has a mix of different digit types. This fossil helps us see how digits shifted during evolution.

A digit is one of the most distal parts of a limb. In many vertebrates, these parts are known as fingers or toes.

The term "digit" is used by scientists to describe these structures generally. In English, we use specific words like "finger" for hands and "toe" for feet. However, many other languages do not make this distinction. For example, Arabic, Russian, and Spanish speakers use phrases like "digit of the hand" instead. In Japanese, the word "yubi" can refer to either fingers or toes depending on the context.

In humans, we normally have five digits on each extremity. Each individual digit is composed of several bones called phalanges. These bones are surrounded by soft tissue to form the digit. On human fingers, there is typically a nail located at the distal phalanx, which is the very end of the finger. Sometimes, the number of digits can vary due to biological mutations. Polydactyly is the term for when extra digits are present. Conversely, ectrodactyly refers to having fewer digits than normal. A famous example is the chess world champion Mikhail Tal, who lived with only three fingers on his right hand.

The brain maintains a complex relationship with our digits through a process of mapping. Each finger has an orderly somatotopic representation in the somatosensory cortex. Specifically, these maps are found in area 3b, which is part of area 1. There are also overlapping representations in the primary motor area and the supplementary motor area. This cortical map is a dynamic reflection of the physical fingers on the hand. This means that the brain's map changes based on the actual state of the digits.

This brain mapping becomes very interesting when studying conditions like syndactyly. In syndactyly, a person is born with a clubhand where the fingers are webbed or shortened. Because the fingers are physically fused, the cortical maps in the brain also form a fused club hand. Surgeons can sometimes perform operations to divide these fingers to make the hand more useful. At the Institute of Reconstructive Plastic Surgery in New York, surgeons treated a 32-year-old man named O. G. They used MRI brain scans to monitor his progress. Before the surgery, his brain maps were fused together. After the surgery, the maps of his individual fingers separated into a normal layout.

Scientists also study the long history of how digits evolved from ancient fish. There are two main ideas regarding the homology of limbs. One idea is that digits are unique to tetrapods, which are animals with four limbs. The second idea is that the ancestors of digits were already present in the fins of early sarcopterygian fish. For a long time, few transitional fossils were known to show this change.

A coastal fish called Panderichthys lived during the Devonian period, about 385 million years ago. A 2008 study by Boisvert et al. discovered that Panderichthys had at least four fin radials. These bones are similar to rudimentary fingers. This suggests that the outermost fin rays were lost and replaced by inner radials that evolved into digits.

Other prehistoric creatures provide more evidence for this evolutionary transition. Tiktaalik is a well-known Devonian vertebrate often called a "missing link" between fish and tetrapods. Tiktaalik possessed several rows of digit-like distal fin radials. Another fish, Elpistostege, shows an even more advanced structure. The hand of Elpistostege had 19 distal fin radials arranged into blocks. These blocks could be up to four radials long and are very similar to modern digits. While the fish Sauripterus also had digit-like radials, this is likely a case of convergent evolution rather than a direct link.

The evolution of digits is also visible in the transition from dinosaurs to birds. Birds and theropod dinosaurs typically have three digits on their hands. However, the specific digits involved differ between the two groups. The bird hand is embedded in the wing and is thought to come from the second, third, and fourth digits. In contrast, theropod dinosaurs seem to have possessed the first, second, and third digits. A fossil named Limusaurus found in the Junggar Basin of China shows a complex mix of these traits. It has a first digit stub but also possesses the second, third, and fourth digits. This discovery suggests that bird digit evolution involved a shift in digit identity during early theropod stages.