Hand

The hand is a portion of the arm or anterior limb[?] of a human or other primate, at where the appendage[?] terminates. This part of the limb is especially used in grasping and holding. The left hand is the mirror image of the right hand.

Table of contents 1 What constitutes a hand? 2 Structure of the Hand 2.1 Digits 2.1.1 The Four Fingers 2.1.2 The Thumb 2.2 Bones 2.2.1 Bones of the wrist 2.2.2 Bones of the palm 2.2.3 Digital bones 2.3 Muscles and Tendons 2.3.1 The Flexors 2.3.2 The Extensors 3 Articulation 4 Common uses in English language

What constitutes a hand? Although many mammals and other animals have grasping appendages[?] similar in form to a hand, these are scientifically not considered to be so, and have other varying names, including paws[?]. Using the term hand is merely a scientific usage of anthropomorphization, to distinguish the terminations of the front paws from the hind ones. The only true hands appear in the mammalian order of primates. Hands must also feature opposable thumbs, as described later in the text.

Structure of the Hand The hand consists of a broad palm (metacarpus) with five digits, attached to the forearm by a joint called the wrist (carpus).

Digits

The Four Fingers

The four fingers on the hand are located at the outermost edge of the palm. These four digits can be folded over the palm, this allows for the holding of objects, and furthermore the grasping of small objects.

The Thumb

The thumb (connected to the trapezium) is located on one the sides, parallel to the arm. The thumb can be easily rotated 90º, on a perpendicular level compared to the palm, unlike the fingers which can only be rotated approximately 45º. A reliable way of identifying true hands is from the presence of opposable thumbs. Other than opossums (Daubentoniidae), lemurs (Daubentoniidae) and the now extinct dinosaurs, this is a unique feature. Opposable thumbs are identified by the ability to be brought opposite to the fingers.

Bones

The human hand has 27 bones: the carpus or wrist account for 8; the metacarpus or palm contains 5; the remaining 14 are digital bones.

Bones of the wrist

The wrist has eight bones, arranged in two rows of four. These bones fit into a shallow socket formed by the bones of the forearm.

Bones of the palm

The palm has 5 bones, one to each of the 5 digits.

Digital bones

Also called phalanges, hands contain 14 of them; 2 in the thumb, and 3 in each of the four fingers.

Muscles and Tendons

The movements of the human hand are accomplished by two sets of each of these tissues.

The Flexors

Located on the underside of the forearm, attached by tendons to the phalanges of the fingers, these allow for the actual bending of the fingers and thumb. The human thumb has to such muscles, moving the thumb in opposition, making grasping possible.

The Extensors

Located on the back of the forearm and a connected similarly to the flexors. Unlike flexors, they are used to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box.

Articulation Also of note is that the articulation of the human hand is more complex and delicate than that of comparable organs in any other animals. Without this extra articulation, we would not be able to operate a wide variety of tools and devices. The hand can also form a fist[?], for example in combat, or as a gesture.

See also: Common uses in of the word hand in the English language[?], hand (clock)[?], hand (measurement), hand (mechanisms)[?], hand (language)[?].

Common uses in English language I know it like the back of my hand - English phrase used to say that the subject knows the matter perfectly, as if it was part of their body, or that they were born with the knowledge. Related: Second hand.

Second hand - Similar to "I know it like the back of my hand," in that it is definitely known by the subject. Similar to something being described as second nature. Not to be confused with second-hand goods[?], which have already been used before, and are being resold.

A man may also describe somebody as his right hand man, which means that he relies heavily on this person.

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A hand is also:

• A measurement of length, primarily used for the height of horses, see hand (unit of length).
• Something that is like a human hand, such as the rotating pointer on the face of a clock with analog display[?] or on a gauge or dial (hand (mechanisms)[?]).
• A hand (language)[?] used in print materials, which is used to call attention to a particular paragraph or point; a lateral direction, (for example, "there is a button malfunctioning on the right hand side of the remote control."), hand (direction)[?].