Phalanx - definition, types and functions

Digital bones in the arms and legs of most vertebrates

"Phalanx" redirects here. For other uses, see Phalanx (disambiguation).

Into the phalanx

/eəlændʒiz/ (singular:
phalanges
/eælæŋks/) are the digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges, while the other fingers have three phalanges. The phalanges are classified as long bones.

Structure [edit]

Phalanges in the human hand
Phalanges are the bones that make up the fingers and toes. There are 56 phalanges in the human body, fourteen on each arm and leg. Each finger and foot have three phalanges, with the exception of the big toe and great toe, which have only two. The middle and distal phalanges of the fourth and fifth toes often grow together (sympalangism). [1] The phalanges of the hand are commonly called 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 closest to the torso.

The phalanx is named depending on whether it is proximal, middle or distal, and the finger or toe associated with it. The proximal phalanges are those closest to the hand or foot. In the hand, the protruding knobby ends of the phalanges are known as knuckles. The proximal phalanges connect to the metacarpal bones of the hand or metatarsal bones of the foot at the metacarpophalangeal joint or metatarsophalangeal joint. The intermediate phalanx is not only intermediate in location, but usually also in size. The big toe and big toe do not have a middle phalanx. The distal phalanges are the bones at the tips of the fingers or toes. The proximal, intermediate and distal phalanges are connected to each other through the interphalangeal joints. [2] : 708–711 : 708–711

Bone anatomy [edit]

Each phalanx consists of a central part called the body

, and two limbs.

• The body
  is flat on both sides, concave on the palmar surface, and convex on the dorsal surface. On its sides there are uneven areas that give attachment to the fibrous membranes of the flexor tendons. It tapers down from the top.
• At the proximal ends
  of the bones of the first row are true ovals, the concave articular surfaces are wider from side to side than from anterior to posterior. The proximal end of each of the bones of the second and third rows is a double concavity separated by a median ridge.
• The distal ends
  are smaller in size than the proximal one, and each end of the two condyles (joints) are separated from each other by a shallow groove; the articular surface extends further on the palmar surface than on the dorsal surface, and this condition is best expressed in the bones of the first row.

In the foot, the proximal phalanges have a body that is compressed from side to side, convex at the top and concave at the bottom. The base is concave and the head provides a blocking surface for articulation with the second phalanx. The middle is very small and short, but wider than the proximal one. The distal phalanges are smaller than the distal phalanges of the finger and flattened from top to bottom; each presents a broad base for articulation with a corresponding bone of the second row and an extended distal limb to support the nail and the end of the toe.

Distal phalanx[edit]

In the hand, the distal phalanges are flat on the palmar surface, small and with a rough, raised, horseshoe-shaped surface on the palmar surface supporting the pulp of the finger. [3] : 6b. 3. Phalanges of the hand. The flat, wide projections at the ends of the distal phalanges are called apical fascicles. They support your fingertips and nails. [4] The phalanx of the thumb has a pronounced attachment of the flexor pollicis longus (asymmetrical with respect to the radial side), a claw fossa and a pair of unequal nail spines (the ulnar root is more prominent). This asymmetry is necessary to ensure that the pulp of the thumb always faces the pulp of the other fingers, and the osteological configuration provides maximum contact surface with objects being held. [5]

In the foot, the distal phalanges are flat on their dorsal surface. It is largest proximally and tapers towards the distal end. The proximal portion of the phalanx provides a broad base for articulation with the middle phalanx and an extended distal limb to support the nail and the end of the toe. [3] : 6b. 3. Phalanges of the foot. The phalanx ends in a rough, crescent-shaped epiphyseal cap, an apical tuft (or tuberosity/nail process) that covers more of the phalanx on the palmar side than on the dorsal side. Two lateral nail spines project proximally from the apical tuft. At the base of the rod there are two lateral tubercles. Between them a V-shaped protrusion extends proximally, serving for the insertion of the flexor pollicis longus. Another ridge at the base serves to attach the extensor aponeurosis. [6] The insertion of the flexor muscle is formed by two fossae—the nail fossa distally and the proximopalmar fossa proximally.

Development[edit]

The number of phalanges in animals is often expressed as the "phalanx formula", which indicates the number of phalanges in numbers starting from the innermost medial or proximal. For example, humans have a 2-3-3-3-3 formula for the hand, meaning that the thumb has two phalanges and the other fingers have three.

In the distal phalanges of the hand, the centers of the bodies appear at the distal ends of the phalanges, and not in the middle of the bodies, as on other phalanges. Moreover, of all the bones of the hand, the distal phalanges are the first to ossify. [3] : 6b. 3. Phalanges of the hand.

Vestigial phalanges

The evolution of mammals gave a phalangeal formula of 14 bones per limb. However, in many taxa one or more digits have lost their direct function. Dogs, cats, cattle and many other ungulates have a big toe called a dewclaw. This phalanx is not usually used during movement.

In some monkeys, such as colobus monkeys, the thumb is vestigial. Many anteaters, armadillos and sloths have vestigial or missing phalanges. The giant armadillo and the nine-barred armadillo have vestigial fifth toes. In arboreal three-toed sloths there are no two numbers with accompanying phalanges, since they are not important for the animal’s lifestyle. The giant anteater has a fifth finger with only 2 phalanges. In lesser anteaters and silky anteaters, the fifth digit has lost all its phalanges.

• arboreal – Referring to organisms (especially animals) that live in trees.
• condyle - A spherical extension at the end of some bones that forms an interface with another bone.
• digit – Derived from the Latin word “digitus,” it refers to structures found on the extremities of limbs, such as fingers or toes.
• vestigial - Parts of the body that have lost function during evolution, although they are found as essential body parts in other, related species.

History of the phalanx[edit]

Etymology[edit]

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

In animals [edit]

Most land mammals, including humans, have a 2-3-3-3-3 formula in both their hands (or paws) and feet. Primitive reptiles typically had the formula 2-3-4-4-5, and this pattern, with some modifications, has been retained in many later reptiles and in mammal-like reptiles. The formula of the phalanges in the flipper of cetaceans (marine mammals) varies widely from - hyperphalangy (increase in the number of phalangeal bones in numbers). Humpback whales, for example, have a phalangeal formula of 0/2/7/7/3; for pilot whales the formula is 1/10/7/2/1. [7]

In vertebrates, the proximal phalanges have a similar arrangement in the corresponding limbs, be it a paw, wing or fin. In many species it is the longest and thickest phalanx ("finger" bone). The middle phalanx also corresponds to a location in their limbs, be it a paw, wing, hoof or fin.

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

Primates [edit]

Morphological comparisons of pollic distal phalanges in African apes, modern humans, and selected hominins. Note that, although with some morphological differences, all features associated with advanced manipulation in modern humans are already present in the Late Miocene Orrorin. [5]

The morphology of the distal phalanges of the human thumbs closely reflects adaptation to an improved precision grip with pad-to-pad contact. This is traditionally associated with the appearance of stone tools. However, the internal proportions of australopith hands and the similarities between human hands and the short hands of Miocene apes suggest that the proportions of human hands are largely plesiomorphic (as in ancestral species)—as opposed to a derived pattern of an outstretched arm and a poorly developed thumb. musculature of other modern hominoids. [5]

In Neanderthals, the apical fascicles were expanded and more durable than in modern and early Upper Paleolithic people. The suggestion that Neanderthal distal phalanges were an adaptation to colder climates (than in Africa) is not supported by a recent comparison showing that among hominins, cold-adapted populations had smaller apical tufts than warm-adapted populations.[8]

In living non-human primates, the apical fascicles vary in size, but they are never larger than in humans. Enlarged apical fascicles, to the extent that they actually reflect expanded digital pulp, may have played a significant role in increasing friction between the hand and objects in the hands during Neolithic tool making. [4]

In nonhuman primates, phylogeny and locomotion style appear to play a role in the size of the apical fascicle. Suspended primates and New World monkeys have the smallest apical tufts, while terrestrial tetrapods and Strepsirrhines have the largest. [8] A study of the morphology of the fingertips of four species of small-bodied monkeys from the New World showed a correlation between increased foraging on small branches and decreased flexor and extensor tubercles in the distal phalanges and widened distal portions of the distal phalanges combined with widened apical pads. and developed epidermal ridges. This suggests that expanded distal phalanges were developed in arboreal primates rather than in quadrupedal terrestrial primates. [9]

Other mammals[edit]

Skeleton of an orangutan, dog, pig, cattle, tapir and horse

In ungulates (ungulates), the forelimb is optimized for speed and endurance through a combination of stride length and fast stride; the proximal segments of the forelimbs are short with large muscles, and the distal segments are elongated with less muscle. In the two main groups of ungulates, the odd-toed and even-toed ungulates, what remains of the “hands”—the metacarpals and phalanges—are elongated to the point that they are of little use except for locomotion. The giraffe, the largest artiodactyl, has large terminal phalanges and fused metacarpals, capable of absorbing the stress of work. [10]

The sloth spends its life hanging up and down from branches, and has highly specialized third and fourth digits for this purpose. They have short and squat proximal phalanges with much longer terminal phalanges. They have vestigial second and fifth metacarpals, and their palm extends to the distal interphalangeal joints. The arboreal specialization of these terminal phalanges does not allow the sloth to walk on the ground, and the animal is forced to drag its body with its claws. [10]

• Distal phalanges of a Maasai giraffe
• Three-toed sloth
• Terminal phalanx of the ground sloth Scelidotherium

Functions of the phalanx

These bones form the structure of the fingers and toes and are critical to much of hominid evolutionary activity. view, Tool making, precision grasping, grasping and handling of equipment arose from the anatomical features of the phalanges. The contralateral thumb is due to the evolution of the tendon and ligament structure surrounding the bones. A number of changes in the anatomy of the distal phalanx of the thumb are necessary for fine motor movement.

In other animals, phalanges are adapted for rapid movement (horses and giraffes), for locomotion (arboreal mammals), for flight (wings in bats, birds), for swimming (fins in aquatic species) and for hunting (claws) and paws in carnivores).

Links[edit]

1. ↑
   Williams, Linda (22 June 2012).
   "Biphalangeal fifth toe - a 'common variant'". news-medical.net
   . Retrieved July 14, 2014.
2. Drake, Richard L.; Fogle, Wayne; Tibbits, Adam W. M. (2005). Gray's Anatomy for Students
   . Illustrations by Richard Mitchell and Paul Richardson. Philadelphia: Elsevier/Churchill Livingston. ISBN 978-0-8089-2306-0.
3. ^ abc Gray, Henry (1918). Anatomy of the human body. ISBN 0-8121-0644-X.
4. ^ ab "Apical bundles of phalanges". Center for Academic Research and Training in Anthropogenesis. Retrieved January 28, 2017. The fascicles support the fleshy palmar pad (also known as the distal pulp) on the palmar (volar) surface of the finger, as well as the nail on the dorsal surface.
5. ^ abcd Almesia, Sergio; Moya-Sola, El Salvador; Alba, David M.; Streit, David S. (July 22, 2010). "Early origins of humanoid precision grasping: a comparative study of pollic distal phalanges in fossil hominins". PLoS ONE
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6. Shrewsbury and Johnson 1975, p. 784 harvnb error: no target: CITEREFShrewsburyJohnson1975 (help)
7. Cooper et al., "Review and experimental assessment of the embryonic development and evolutionary history of fin and hyperphalanx development in dolphins (Cetaceans: Mammalia)", ResearchGate
   , DOI: 10.1002/dvg.23076. October 2021
8. ^a b Mittra, ES; Smith, V. C.; Lemelin, P; Jungers, W. L. (December 2007). "Comparative morphometry of the primate apical fasciculus". American Journal of Physical Anthropology
   .
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   (4):449–59. DOI: 10.1002/ajpa.20687. PMID 17657781.
9. Hamrick, MW (June 1998). "Functional and adaptive significance of primate pads and claws: evidence from New World anthropoids." American Journal of Physical Anthropology
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   (2):113–27. DOI:10.1002/(SICI)1096-8644(199806)106:2 <113::AID-AJPA2>3.0.CO; 2-R. PMID 9637179.
10. ^ ab Gough-Palmer, Anthony L.; McLachlan, Jody; Routh, Andrew (March 2008). "Paws to Think About: Comparative Radiological Anatomy of the Mammalian Forelimbs". RadioGraphics
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    (2):501–510. DOI: 10.1148/rg.282075061. PMID 18349453.