In the

human body The human body is the entire structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently Organ (biology), organs and then Organ system, org ...

, the tarsus (: tarsi) is a cluster of seven articulating

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s in each

foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...

situated between the lower end of the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

and the

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

of the lower leg and the metatarsus. It is made up of the midfoot (

cuboid In geometry, a cuboid is a hexahedron with quadrilateral faces, meaning it is a polyhedron with six Face (geometry), faces; it has eight Vertex (geometry), vertices and twelve Edge (geometry), edges. A ''rectangular cuboid'' (sometimes also calle ...

, medial, intermediate, and lateral

cuneiform Cuneiform is a Logogram, logo-Syllabary, syllabic writing system that was used to write several languages of the Ancient Near East. The script was in active use from the early Bronze Age until the beginning of the Common Era. Cuneiform script ...

, and navicular) and hindfoot ( talus and

calcaneus In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel; : calcanei or calcanea) or heel bone is a bone of the Tarsus (skeleton), tarsus of the foot which constitutes the heel. In some other ...

). The tarsus articulates with the bones of the metatarsus, which in turn articulate with the

proximal phalanges The phalanges (: phalanx ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. Struct ...

of the toes. The joint between the tibia and fibula above and the tarsus below is referred to as the ankle joint proper. In humans the largest bone in the tarsus is the calcaneus, which is the weight-bearing bone within the heel of the foot.

Human anatomy

Bones

The

talus bone The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of Foot#Structure, foot bones known as the tarsus (skeleton), tarsus. The tarsus forms the lower part of the ankle joint. It transmit ...

or ankle bone is connected superiorly to the two bones of the lower leg, the tibia and fibula, to form the

ankle joint The ankle, the talocrural region or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joint. Th ...

or talocrural joint; inferiorly, at the

subtalar joint In human anatomy, the subtalar joint, also known as the talocalcaneal joint, is a joint of the foot. It occurs at the meeting point of the talus and the calcaneus. The joint is classed structurally as a synovial joint, and functionally as a pl ...

, to the calcaneus or heel bone. Together, the talus and calcaneus form the hindfoot.Podiatry Channel, ''Anatomy of the foot and ankle'' The five irregular bones of the midfoot—the

, navicular, and three

bones—form the

arches of the foot The arches of the foot, formed by the tarsal and metatarsal bones, strengthened by ligaments and tendons, allow the foot to support the weight of the body in the erect posture with the least weight. They are categorized as longitudinal and t ...

which serves as a shock absorber. The midfoot is connected to the hind- and forefoot by muscles and the

plantar fascia The plantar fascia or plantar aponeurosis is the thick connective tissue aponeurosis which supports the Arches of the foot, arch on the bottom (plantar side) of the foot. Recent studies suggest that the plantar fascia is actually an aponeurosis r ...

Movements

The complex motion of the subtalar joint occurs in three planes and produces subtalar inversion and eversion. Along with the transverse tarsal joint (i.e. talonavicular and calcaneocuboid joint), the subtalar joint transforms tibial rotation into forefoot

supination Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

and

pronation Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

. The axis of rotation in the joint is directed upward 42 degrees from the horizontal plane and 16 degrees medially from the midline of the foot. However, together, the subtalar facets form a screw or

Archimedean spiral The Archimedean spiral (also known as Archimedes' spiral, the arithmetic spiral) is a spiral named after the 3rd-century BC Ancient Greece, Greek mathematician Archimedes. The term ''Archimedean spiral'' is sometimes used to refer to the more gene ...

(right-handed in the right foot) about which subtalar motion occurs. So, during subtalar inversion, the calcaneus also rotates clockwise and translates forward along the axis of the screw. Average subtalar motion is 20-30 degrees inversion and 5-10 degrees eversion. Functional motion during the

gait Gait is the pattern of Motion (physics), movement of the limb (anatomy), limbs of animals, including Gait (human), humans, during Animal locomotion, locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on s ...

cycle is 10-15 degrees (the heel strikes the ground in slight inversion followed by quick eversion). Nordin-Frankel 2001, pp 229-30 The talonavicular and calcaneocuboid joints (i.e. between the talus and navicular bones, and the calcaneus and cuboid bones) form the so-called transverse tarsal joint or Chopart's joint. It has two axes of motion. Inversion and eversion occur about a longitudinal axis oriented 15 degrees upward from the horizontal plane and 9 degrees medially from the longitudinal axis of the foot. Flexion and extension occur primarily about an oblique axis oriented 52 degrees upward from the horizontal plane and 57 degrees anteromedially (forward-inward). ''

In vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

'' talonavicular motion is 7 degrees flexion-extension and 17 degrees pronation-supination; while calcaneocuboid motion is 2 degrees flexion-extension and 7 degrees pronation-supination. The motions of the subtalar and transverse talar joints interact to make the foot either flexible or rigid. With the subtalar joint in eversion, the two joints of the transverse joint are parallel, which make movements in this joint possible. With the subtalar joint in inversion, the axes of the transverse joint are convergent, movements in this joint are thus locked and the midfoot rigid.

Other animals

In primitive

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s, such as '' Trematops'', the tarsus consists of three rows of bones. There are three proximal tarsals, the tibiale, intermedium, and fibulare, named for their points of articulation with the bones of the lower limb. These are followed by a second row of four bones, referred to as the centralia (singular: centrale), and then a row of five distal tarsals, each articulating with a single metatarsal. In the great majority of tetrapods, including all of those alive today, this simple pattern is modified by the loss and fusion of some of the bones.Romer-Parsons 1977, pp 205-208 In reptiles and mammals, there are normally just two proximal tarsals, the calcaneus (equivalent to the amphibian fibulare) and the talus (probably derived from a fusion of multiple bones). In mammals, including humans, the talus forms a hinge joint with the tibia, a feature especially well developed in the

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

s. The calcaneus is also modified, forming a heel for the attachment of the

Achilles tendon The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcane ...

. Neither of these adaptations is found in reptiles, which have a relatively simple structure to both bones. The fifth distal tarsal disappears relatively early in evolution, with the remainder becoming the cuneiform and cuboid bones. Reptiles usually retain two centralia, while mammals typically have only one (the navicular). In birds, the tarsus has disappeared, with the proximal tarsals having fused with the tibia, the centralia having disappeared, and the distal bones having fused with the metatarsals to form a single

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bird bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) a ...

bone, effectively giving the leg a third segment.

Additional images

Notes

References

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External links

Diagram, identifying bones
* () {{Authority control Short bones Foot Bones of the foot Tarsal bones