intermediate phalanges
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The phalanges (singular: ''phalanx'' ) are
digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of electronics Electronics comprises the physics, engineering, technology a ...
bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, store minerals, provide str ...

bone
s in the
hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hand
s and
feet The foot (plural: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a Limb (anatomy), limb which bears weight and allows Animal locomotion, locomotion. In many animals with feet, the foot is a separate org ...

feet
of most
vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...

vertebrates
. In
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural gro ...

primate
s, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as
long bones The long bones are those that are longer than they are wide. They are one of five types of bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs ...
.


Structure

The phalanges are the bones that make up the fingers of the hand and the toes of the foot. There are 56 phalanges in the human body, with fourteen on each hand and foot. Three phalanges are present on each finger and toe, with the exception of the
thumb The thumb is the first digit of the hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is use ...

thumb
and
large toe
large toe
, which possess only two. The middle and far phalanges of the fifth toes are often fused together (symphalangism). The phalanges of the
hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hand
are commonly known as the finger bones. The phalanges of the foot differ from the hand in that they are often shorter and more compressed, especially in the proximal phalanges, those closest to the torso. A phalanx is named according to whether it is
proximal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...
, middle, or
distal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...
and its associated finger or toe. The proximal phalanges are those that are closest to the hand or foot. In the hand, the prominent, knobby ends of the phalanges are known as
knuckle The knuckles are the joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones prot ...

knuckle
s. The proximal phalanges join with the
metacarpal In human anatomy, the metacarpal bones or metacarpus, form the intermediate part of the skeleton, skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist which forms the connection to the forearm. The metacarpal ...
s of the hand or
metatarsal The metatarsal bones, or metatarsus are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...
s of the foot at the
metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavit ...
or
metatarsophalangeal joint The metatarsophalangeal joints (MTP joints), also informally known as toe knuckle The knuckles are the joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a fu ...
. The intermediate phalanx is not only intermediate in location, but usually also in size. The thumb and large toe do not possess a middle phalanx. The distal phalanges are the bones at the tips of the fingers or toes. The proximal, intermediate, and distal phalanges articulate with one another through
interphalangeal joints of hand The interphalangeal joints of the hand are the hinge joints between the phalanges of the fingers that provide flexion towards the palm of the hand. There are two sets in each finger (except in the thumb, which has only one joint): * "proximal i ...
and
interphalangeal joints of the foot The interphalangeal joints of the foot are between the phalanx bones of the toes in the foot, feet. Since the Toe#Hallux, great toe only has two phalanx bones (proximal and distal phalanges), it only has one interphalangeal joint, which is often a ...
.


Bone anatomy

Each phalanx consists of a central part, called the ''body'', and two extremities. * The ''body'' is flat on either side, concave on the palmar surface, and convex on the dorsal surface. Its sides are marked with rough areas giving attachment to fibrous sheaths of flexor tendons. It tapers from above downwards. * The ''proximal extremities'' of the bones of the first row present oval, concave articular surfaces, broader from side to side than from front to back. The proximal extremity of each of the bones of the second and third rows presents a double concavity separated by a median ridge. * The ''distal extremities'' are smaller than the proximal, and each ends in two condyles (knuckles) separated by a shallow groove; the articular surface extends farther on the palmar than on the dorsal surface, a condition best marked in the bones of the first row. In the foot, the proximal phalanges have a body that is compressed from side to side, convex above, and concave below. The base is concave, and the head presents a trochlear surface for articulation with the second phalanx. The middle are remarkably small and short, but rather broader than the proximal. The distal phalanges, as compared with the distal phalanges of the finger, 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.


Distal phalanx

In the hand, the distal phalanges are flat on their palmar surface, small, and with a roughened, elevated surface of horseshoe form on the palmar surface, supporting the finger pulp. The flat, wide expansions found at the tips of the distal phalanges are called apical tufts. They support the fingertip pads and nails. The phalanx of the thumb has a pronounced insertion for the
flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromo ...
(asymmetric towards the radial side), an ungual fossa, and a pair of unequal ungual spines (the ulnar being more prominent). This asymmetry is necessary to ensure that the thumb pulp is always facing the pulps of the other digits, an osteological configuration which provides the maximum contact surface with held objects. In the foot, the distal phalanges are flat on their dorsal surface. It is largest proximally and tapers to the distal end. The proximal part of the phalanx presents a broad base for articulation with the middle phalanx, and an expanded distal extremity for the support of the nail and end of the toe. The phalanx ends in a crescent-shaped rough cap of bone
epiphysis The epiphysis is the rounded end of a long bone, at its joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiol ...
 — the apical tuft (or ungual tuberosity/process) which covers a larger portion of the phalanx on the volar side than on the dorsal side. Two lateral ungual spines project proximally from the apical tuft. Near the base of the shaft are two lateral tubercles. Between these a V-shaped ridge extending proximally serves for the insertion of the
flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large biomolecules or macromo ...
. Another ridge at the base serves for the insertion of the extensor
aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia A fascia (; plural fasciae ; adjective fascial; from Latin: "band") is a band or sheet of connective tissue, primarily collagen, beneath the skin that attaches, ...
. The flexor insertion is sided by two fossae — the ungual fossa distally and the proximopalmar fossa proximally.


Development

The number of phalanges in animals is often expressed as a "phalangeal formula" that indicates the numbers of phalanges in digits, beginning from the innermost medial or proximal. For example, humans have a 2-3-3-3-3 formula for the
hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hand
, meaning that the thumb has two phalanges, whilst the other fingers each have three. In the distal phalanges of the hand the centres for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the distal phalanges are the first to ossify.


Function

The distal phalanges of
ungulate Ungulates ( ) are members of the diverse clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ances ...
s carry and shape nails and
claw A domestic cat's retractable claw in protracted position A claw is a curved, pointed appendage found at the end of a toe or finger in most amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bo ...

claw
s and these in primates are referred to as the ''
ungual An ungual (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman R ...
phalanges''.


History of phalanges


Etymology

The term phalanx or phalanges refers to an ancient Greek army formation in which soldiers stand side by side, several rows deep, like an arrangement of fingers or toes.


In animals

Most land
mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk ...
s including humans have a 2-3-3-3-3 formula in both the
hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hand
s (or
paw A paw is the soft foot-like part of a mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...
s) and
feet The foot (plural: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a Limb (anatomy), limb which bears weight and allows Animal locomotion, locomotion. In many animals with feet, the foot is a separate org ...

feet
. Primitive
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtle ...

reptile
s usually had the formula 2-3-4-4-5, and this pattern, with some modification, remained in many later reptiles and in the
mammal-like reptile The pelycosaurs (pronounced PEL-ih-ko-saurz) were previously considered an order, but are now only an informal grouping composed of basal or primitive Late Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek ''palaiós'' (), "old ...
s. The phalangeal formula in the
flippers Flipper may refer to: Common meanings *Flipper (anatomy), a forelimb of an aquatic animal, useful for steering and/or propulsion in water *Alternate name for a swimfin, footwear that boosts human swimming efficiency *Flipper (pinball), a part of a ...
of
cetaceans Cetaceans (from la, Cetus (mythology), cetus, lit=whale, from grc, κῆτος, translit=Cetus (mythology), kētos, lit = huge fish, sea monster) are aquatic mammals constituting the infraorder Cetacea (). Key characteristics are their fully aq ...

cetaceans
(marine mammals) varies widely due to hyperphalangy (the increase in number of
phalanx bones The phalanges (singular: ''phalanx'' ) are digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of electronics Elect ...
in the digits). In
humpback whales The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale Baleen whales (systematic name Mysticeti), also known as whalebone whales, form a parvorder of the infraorder Cetacea (whales, dolphins and porpoises). They are a wi ...
, for example, the phalangeal formula is 0/2/7/7/3; in
pilot whales Pilot whales are cetacean Cetaceans (from la, cetus, lit=whale, from grc, κῆτος, translit=Cetus (mythology), kētos, lit = huge fish, sea monster) are aquatic mammals constituting the infraorder Cetacea (). Key characteristics are the ...
the formula is 1/10/7/2/1. In vertebrates, proximal phalanges have a similar placement in the corresponding limbs, be they
paw A paw is the soft foot-like part of a mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...
,
wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined Cross section (geometry), cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's Aerody ...

wing
or
fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described quantitatively by Newton' ...

fin
. In many species, they are the longest and thickest phalanx ("finger" bone). The middle phalanx also a corresponding place in their limbs, whether they be
paw A paw is the soft foot-like part of a mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...
,
wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined Cross section (geometry), cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's Aerody ...

wing
,
hoof Cloven hooves of roe deer (''Capreolus capreolus''), with prominent dewclaws A hoof ( or ), plural hooves ( or ) or hoofs , is the tip of a toe of an ungulate mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrat ...
or
fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force described quantitatively by Newton' ...

fin
. The distal phalanges are cone-shaped in most mammals, including most primates, but relatively wide and flat in humans.


Primates

The morphology of the distal phalanges of human thumbs closely reflects an adaptation for a refined precision grip with pad-to-pad contact. This has traditionally been associated with the advent of stone tool-making. However, the intrinsic hand proportions of and the resemblance between human hands and the short hands of
Miocene The Miocene ( ) is the first Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish author Charles Lyell; its name comes from the Greek words (', "less") and (', "new") and means "le ...
apes, suggest that human hand proportions are largely
plesiomorphic File:Cladogram imaginary birds.jpg, Imaginary cladogram. The yellow mask is a plesiomorphy for each living masked species, because it is ancestral. It is also a symplesiomorphy for them. But for the four living species as a whole, it is an apomorph ...
(as found in ancestral species) — in contrast to the derived elongated hand pattern and poorly developed thumb musculature of other extant
hominoid Apes (Hominoidea ) are a branch Image:Tree Leaves.JPG, The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany as a ramus) is a woody structural member connected to but not part of the central ...
s. In
Neanderthal Neanderthals (, also Neandertals, ''Homo neanderthalensis'' or ''Homo sapiens neanderthalensis'') are an extinct species In biology Biology is the natural science that studies life and living organisms, including their anatomy, phys ...
s, the apical tufts were expanded and more robust than in modern and early upper Paleolithic humans. A proposal that Neanderthal distal phalanges was an adaptation to colder climate (than in Africa) is not supported by a recent comparison showing that in
hominin The Hominini form a Tribe (biology), taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and ''Pan (genus), Pan'' (chimpanzees and bonobos), but excludes the genus ''Gorilla'' (gorillas). ...
s, cold-adapted populations possessed smaller apical tufts than do warm-adapted populations. In non-human, living primates the apical tufts vary in size, but they are never larger than in humans. Enlarged apical tufts, to the extent they actually reflect expanded digital pulps, may have played a significant role in enhancing friction between the hand and held objects during Neolithic toolmaking. Among non-human primates
phylogenesis Phylogenesis (from Greek φῦλον ''phylon'' "tribe" + γένεσις ''genesis'' "origin") is the biological process by which a taxon In biology Biology is the natural science that studies life and living organisms, including their a ...
and style of locomotion appear to play a role in apical tuft size. Suspensory primates and
New World monkey New World monkeys are the five families of primate A primate ( ) (from Latin , from 'prime, first rank') is a eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade A clade (; from grc, , ''klados'', "branch ...
s have the smallest apical tufts, while terrestrial quadrupeds and
Strepsirrhines Strepsirrhini or Strepsirhini (; ) is a suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks ...

Strepsirrhines
have the largest. A study of the fingertip morphology of four small-bodied New World monkey species, indicated a correlation between increasing small-branch foraging and reduced flexor and extensor tubercles in distal phalanges and broadened distal parts of distal phalanges, coupled with expanded apical pads and developed epidermal ridges. This suggests that widened distal phalanges were developed in arboreal primates, rather than in quadrupedal terrestrial primates.


Other mammals

In
ungulate Ungulates ( ) are members of the diverse clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ances ...
s (hoofed mammals) the forelimb is optimized for speed and endurance by a combination of length of stride and rapid step; the proximal forelimb segments are short with large muscles, while the distal segments are elongated with less musculature. In two of the major groups of ungulates, odd-toed and even-toed ungulates, what remain of the "hands" — the
metacarpal In human anatomy, the metacarpal bones or metacarpus, form the intermediate part of the skeleton, skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist which forms the connection to the forearm. The metacarpal ...
and phalangeal bones — are elongated to the extent that they serve little use beyond locomotion. The
giraffe The giraffe is a tall African mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Fe ...

giraffe
, the largest even-toed ungulate, has large terminal phalanges and fused metacarpal bones able to absorb the stress from running. The
sloth Sloths are a group of arboreal Neotropical xenarthran mammals, constituting the suborder Folivora. Noted for their slowness of movement, they spend most of their lives hanging upside down in the trees of the tropical rainforest File:Kop ...

sloth
spends its life hanging upside-down from branches, and has highly specialized third and fourth digits for the purpose. They have short and squat proximal phalanges with much longer terminal phalanges. They have
vestigial is a vestigial structure; it has lost much of its ancestral function. Vestigiality is the retention during the process of evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations o ...
second and fifth metacarpals, and their palm extends to the distal interphalangeal joints. The arboreal specialization of these terminal phalanges makes it impossible for the sloth to walk on the ground where the animal has to drag its body with its claws.


Additional images

File:Q11.jpg, Phalanges. File:Carpus2.jpg, Phalanges. File:Extra phalangeal crease.jpg, Extra phalangeal crease File:Unilateral extra phalangeal crease.jpg, Unilateral extra phalangeal crease File:814 Radiograph of Hand.jpg, Joints of the hand in an X-ray image File:Finger phalanges movement.png, Movement of the three finger phalanges; Distal, middle and proximal


See also

*
Hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

Hand
*
Foot The foot (plural: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a Limb (anatomy), limb which bears weight and allows Animal locomotion, locomotion. In many animals with feet, the foot is a separate org ...

Foot


References


External links


MedTerms.com Medical Dictionary
{{Authority control Long bones Vertebrate anatomy