Hand and Foot
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Wikipedia-Article "Hand"
- For other uses, see Hand (disambiguation).
The hand (med./lat.: manus) is the portion of the arm or anterior limb of a human or other primate, where the appendage terminates. This part of the limb is especially used in grasping and holding. Each hand is a mirror image of the other.
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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.
Human anatomy of the hand
The human hand consists of a broad palm (metacarpus) with five digits, attached to the forearm by a joint called the wrist (carpus).
Digits
The Five Fingers
Five 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. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:
- thumb
- index finger, pointer finger, or forefinger
- middle finger
- ring finger
- little finger or 'pinky'
The thumb
The thumb (connected to the trapezium) is located on one of 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. Opposable thumbs are identified by the ability to be brought opposite to the fingers.
Bones
The human hand has at least 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 phalanx bones. Human hands contain 14 of them; 2 in the thumb, and 3 in each of the four fingers, called;
- distal phalanx, carrying the nail,
- middle phalanx and
- proximal phalanx.
(The thumb has no middle phalanx).
Sesamoid bones
Sesamoid bones are small ossified nodes embedded in the tendons to provide extra leverage and reduce pressure on the underlying tissue. Many exist around the palm at the bases of the digits, but the exact number varies between different people. The patella is the largest example of a sesamoid bone in the human body.
Muscles and tendons
The movements of the human hand are accomplished by two sets of each of these tissues. They can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm.
Intrinsic hand muscles
The Intrinsic muscle groups are the thenar and hypothenar muscles (thenar referring to the thumb, hypothenar to the small finger), the interosseus muscles (between the metacarpal bones, four dorsally and three volarly) and the lumbrical muscles. These muscles arise from the deep flexor (and are special because they have no bony origin) and insert on the dorsal extensor hood mechanism.
The extrinsic muscles of the hand
The flexors
The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens- and abductor muscle), moving the thumb in opposition, making grasping possible.
The extensors
Located on the back of the forearm and a connected in a more complex way then the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor, used for instance for pointing.
Variation
Some people have more than the usual number of fingers or toes, this is normally caused by a genetic condition called Polydactyly.
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 of the word hand in the English language, hand (clock), hand (unit), hand (mechanisms), hand (language).
Common uses in the 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 were 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. In the U.S., at least, second hand means indirect--almost the opposite. "She told me walking everyday is good for the brain" indicates second hand knowledge.
A person may also describe somebody as his right hand man, which means that he relies heavily on this person, deriving from the importance and superiority place on the right over the left by many civilizations. Exemplified by phrases such as 'he is my right hand' and 'to be seated at the right hand of the gods when Judgment comes'.
The hand is also an archaic unit of measurement.
Phalanx Bones
The name Phalanges is commonly given to the bones that form fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three.
The phalanges do not really have individual names but are named after the digit, and their distance from the body. Distal phalanges are at the tips of the fingers and toes, the proximal phalanges are closest to the hand (or foot) and articulate with the metacarpals or metatarsals. Middle phalanges are between the distal and proximal. The thumb and big toe do not have middle phalanges.
The phalanges of the foot correspond with those of the hand. They differ from them in their size (the bodies being much reduced in length) and being laterally compressed.
First Row, The body of each is compressed from side to side, convex above, concave below. The base is concave; and the head presents a trochlear surface for articulation with the second phalanx.
Second Row, The phalanges of the second row are remarkably small and short, but rather broader than those of the first row.
The ungual phalanges, in form, resemble those of the fingers; but they are smaller and are flattened from above downward; each presents a broad base for articulation with the corresponding bone of the second row, and an expanded distal extremity for the support of the nail and end of the toe.
The phalanges are each ossified from two centers: one for the body, and one for the base. The center for the body appears about the tenth week, that for the base between the fourth and tenth years; it joins the body about the eighteenth year.
See also
Wikipedia-Article "Foot"
- For other uses, see Foot (disambiguation).
The foot is a biological structure found in many animals that is used for locomotion. The plural of foot is feet, and this pair is one of seven mutated English plurals.
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Structure
The structural quality of a foot varies from animal to animal. Many vertebrates that have legs also have a foot located at the end of each leg. For these animals, the foot is a complex structure of bone, muscle, and other connective tissue. Among animals that have soft or padded feet, the foot is commonly called a paw. In mollusks, on the other hand, the foot is a purely muscular structure.
Human beings use their legs and feet for bipedal locomotion, also known as walking. The structures of the human foot and hand are variations on the same basic five-digit anatomy, in common with many other vertebrates (the thumb and big toe have two phalanges, while the other fingers and toes consist of three). They are also the most complex, comprising half the bones in the body. The medical specialty related to treatment of the feet is podiatry.
Foot covering
In many societies, it is customary to cover the foot in most social situations; particularly outside, in many cultures (including North American, European, Japanese and others) people wear protective clothing over the foot. Such footwear has special names, such as sandals, shoes, and boots. Consistent wearing of footwear, particularly in hot climates or during exercise, can lead to foot odor. If footwear is ill-fitting or badly designed, it can cause both short-term (blisters, for example) and long-term foot problems. On the other hand, carefully designed orthopedic footwear is an effective treatment for many foot, leg, and back problems.
Customs
Customs about foot covering while indoors vary significantly from place to place. For example, in much of Europe and Canada, it is customary to remove one's shoes or boots when entering a home, while in the United States this is rare in most parts of the country. In Japan, the custom is so widespread that floors are often made of materials that are too soft to survive being walked on by shoed feet. In some cultures, bare feet may be considered unsightly or offensive. In Arab countries and in Thailand, it is considered extremely offensive to show someone the sole of your foot, although the practice of not wearing shoes is common, due to various reasons including poverty and religion.
Kicking
Striking an object or a person with the foot is called kicking. Certain martial arts, such as Savate, emphasize kicking, reasoning that the foot is the only part of the body normally covered by protective clothing. On the other hand, some martial arts (including Karate, Judo) are customarily trained in bare feet, as well as beach sport (for example beach volleyball). Many sports, including football (in all its forms, including soccer), and rugby, involve kicking a ball or other object with the foot.
Measurement
The foot provides a convenient way to measure short distances on the ground, by placing one foot directly in front of the other; this led to the adoption of the foot as a unit of length.
Parts of the foot
Parts of the foot
Disorders of the feet
See also
External links
- American College of Foot and Ankle Surgeons
- American Podiatric Medical Association
- American Board of Podiatric Surgery
- American Academy of Podiatric Sports Medicine
- American Orthopedic Foot and Ankle Society
- http://www.podiatrytoday.com/podtd/
- http://www.epodiatry.com/foot_problems.htm
- http://www.barefooters.org/
- http://www.unshod.org/pfbc/