The femur (; ), or thigh bone, is the

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...

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, an ...

of the

hindlimb A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hindl ...

tetrapod Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

s. The head of the femur articulates with the

acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) tha ...

in the

pelvic bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, ischiu ...

forming the

hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...

, while the distal part of the femur articulates with the

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

(shinbone) and

patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as m ...

(kneecap), forming the

knee joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the h ...

. By most measures the two (left and right) femurs are the strongest bones of the body, and in humans, the largest and thickest.

Structure

The femur is the only bone in the upper

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element c ...

. The two femurs converge medially toward the

knee In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest join ...

s, where they articulate with the

ends of the

e. The angle of convergence of the femora is a major factor in determining the

femoral-tibial angle The femoral-tibial angle is the angle between the femur and tibia. In humans, the two femurs converge medially toward the knees, where they articulate with the proximal ends of the tibiae. The angle of convergence of the femora is a major factor i ...

. Human females have thicker

s, causing their femora to converge more than in males. In the condition ''genu valgum'' (knock knee) the femurs converge so much that the knees touch one another. The opposite extreme is ''genu varum'' (bow-leggedness). In the general population of people without either ''genu valgum'' or ''genu varum'', the femoral-tibial angle is about 175 degrees. The femur is the largest and thickest bone in the human body. By some measures, it is also the strongest bone in the human body. This depends on the type of measurement taken to calculate strength. Some strength tests show the temporal bone in the skull to be the strongest bone. The femur length on average is 26.74% of a person's height, a ratio found in both men and women and most ethnic groups with only restricted variation, and is useful in

anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics, in both the present and past, including past human species. Social anthropology studies patterns of be ...

because it offers a basis for a reasonable estimate of a subject's height from an incomplete

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

. The femur is categorised as a long bone and comprises a diaphysis (shaft or

body Body may refer to: In science * Physical body, an object in physics that represents a large amount, has mass or takes up space * Body (biology), the physical material of an organism * Body plan, the physical features shared by a group of anima ...

) and two

epiphyses The epiphysis () is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the j ...

(extremities) that articulate with adjacent bones in the hip and knee.

Upper part

The

upper Upper may refer to: * Shoe upper or ''vamp'', the part of a shoe on the top of the foot * Stimulant, drugs which induce temporary improvements in either mental or physical function or both * ''Upper'', the original film title for the 2013 found fo ...

or proximal extremity (close to the

torso The torso or trunk is an anatomical term for the central part, or the core, of the body of many animals (including humans), from which the head, neck The neck is the part of the body on many vertebrates that connects the head with the tors ...

) contains the

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may no ...

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

, the two trochanters and adjacent structures. The upper extremity is the shortest femoral extremity, the lower extremity is the thickest femoral extremity. The head of the femur, which articulates with the

of the

, comprises two-thirds of a

sphere A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

. It has a small groove, or

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy * Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head *Trochlear fovea of the f ...

, connected through the round ligament to the sides of the

acetabular notch The acetabular notch is a deep notch in the acetabulum of the hip bone. The acetabular notch is continuous with a circular non-articular depression, the acetabular fossa, at the bottom of the cavity: this depression is perforated by numerous ape ...

. The head of the femur is connected to the shaft through the

or ''collum''. The neck is 4–5 cm. long and the diameter is smallest front to back and compressed at its middle. The collum forms an angle with the shaft in about 130 degrees. This angle is highly variant. In the

infant An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used t ...

it is about 150 degrees and in

old age Old age refers to ages nearing or surpassing the life expectancy of human beings, and is thus the end of the human life cycle. Terms and euphemisms for people at this age include old people, the elderly (worldwide usage), OAPs (British usage ...

reduced to 120 degrees on average. An abnormal increase in the angle is known as

coxa valga Coxa valga is a deformity of the hip where the angle formed between the head and neck of the femur and its shaft is increased, usually above 135 degrees. The differential diagnosis includes neuromuscular disorders (i.e. cerebral palsy, spinal dy ...

and an abnormal reduction is called

coxa vara Coxa vara is a deformity of the hip, whereby the angle between the head and the shaft of the femur is reduced to less than 120 degrees. This results in the leg being shortened and the development of a limp. It may be congenital and is commonly ca ...

. Both the head and neck of the femur is vastly embedded in the hip musculature and can not be directly palpated. In skinny people with the

thigh In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of ...

laterally rotated, the head of the femur can be felt deep as a resistance profound (deep) for the

femoral artery The femoral artery is a large artery in the thigh and the main arterial supply to the thigh and leg. The femoral artery gives off the deep femoral artery or profunda femoris artery and descends along the anteromedial part of the thigh in the f ...

. The transition area between the head and neck is quite rough due to attachment of muscles and the hip joint capsule. Here the two trochanters, greater and

lesser trochanter The lesser trochanter is a conical posteromedial bony projection of the femoral shaft. it serves as the principal insertion site of the iliopsoas muscle. Structure The lesser trochanter is a conical posteromedial projection of the shaft of the f ...

, are found. The greater trochanter is almost box-shaped and is the most

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

prominent of the femur. The highest point of the greater trochanter is located higher than the collum and reaches the midpoint of the

. The greater trochanter can easily be felt. The

trochanteric fossa In mammals including humans, the medial surface of the greater trochanter has at its base a deep depression bounded posteriorly by the intertrochanteric crest, called the trochanteric fossa. This fossa is the point of insertion of four muscles. ...

is a deep depression bounded posteriorly by the intertrochanteric crest on the medial surface of the greater trochanter. The lesser trochanter is a cone-shaped extension of the lowest part of the femur neck. The two trochanters are joined by the

intertrochanteric crest The intertrochanteric crest is a prominent bony ridge upon the posterior surface of the femur at the junction of the neck and the shaft of the femur. It extends between the greater trochanter superiorly, and the lesser trochanter inferiorly. Ana ...

on the back side and by the

intertrochanteric line The intertrochanteric line (or ''spiral line of the femur''White (2005), p 256 ) is a line located on the anterior side of the proximal end of the femur. Structure The rough, variable ridge stretches between the lesser trochanter and the greate ...

on the front. A slight ridge is sometimes seen commencing about the middle of the intertrochanteric crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the

linea quadrata A slight ridge is sometimes seen commencing about the middle of the intertrochanteric crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the linea quadrata (or quadrate line), and gives attac ...

(or quadrate line). About the junction of the upper one-third and lower two-thirds on the intertrochanteric crest is the

quadrate tubercle The quadrate tubercle is a small tubercle found upon the upper part of the femur. It serves as a point of insertion of the quadratus femoris muscle, along with the intertrochanteric crest and the linea quadrata. Structure The quadrate tubercle ...

located. The size of the tubercle varies and it is not always located on the intertrochanteric crest and that also adjacent areas can be part of the quadrate tubercle, such as the posterior surface of the greater trochanter or the neck of the femur. In a small anatomical study it was shown that the

epiphyseal line An epiphyseal line is an epiphyseal plate that has become ossified. The process of it forming from an epiphyseal plate is named epiphyseal closure. In adult humans, it marks the point of fusion between the epiphysis and the metaphysis. Funct ...

passes directly through the quadrate tubercle.

Body

The body of the femur (or shaft) is large, thick and almost cylindrical in form. It is a little broader above than in the center, broadest and somewhat flattened from before backward below. It is slightly arched, so as to be convex in front, and concave behind, where it is strengthened by a prominent longitudinal ridge, the

linea aspera The linea aspera ( la, rough line) is a ridge of roughened surface on the posterior surface of the shaft of the femur. It is the site of attachments of muscles and the intermuscular septum. Its margins diverge above and below. The linea aspera ...

which diverges proximally and distal as the medial and lateral ridge. Proximally the lateral ridge of the linea aspera becomes the

gluteal tuberosity The gluteal tuberosity is the lateral one of the three upward prolongations of the linea aspera of the femur, extending to the base of the greater trochanter. It serves as the principal insertion site for the gluteus maximus muscle. Structure ...

while the medial ridge continues as the pectineal line. Besides the linea aspera the shaft has two other bordes; a lateral and medial border. These three bordes separates the shaft into three surfaces: One

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

, one medial and one lateral. Due to the vast musculature of the thigh the shaft can not be palpated. The third trochanter is a bony projection occasionally present on the proximal femur near the superior border of the gluteal tuberosity. When present, it is oblong, rounded, or conical in shape and sometimes continuous with the gluteal ridge. A structure of minor importance in humans, the incidence of the third trochanter varies from 17–72% between ethnic groups and it is frequently reported as more common in females than in males.

Lower part

The

lower extremity of the femur The lower extremity of femur (or distal extremity) is the lower end of the femur (thigh bone) in human and other animals, closer to the knee. It is larger than the upper extremity of femur, is somewhat cuboid in form, but its transverse diameter is ...

(or distal extremity) is the thickest femoral extremity, the

upper extremity The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulde ...

is the shortest femoral extremity. It is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior (front to back). It consists of two oblong eminences known as the

condyles A condyle (;Entry "condyle"
in
Intercondylar fossa of femur, is present between them. The lateral condyle is the more prominent and is the broader both in its antero-posterior and transverse diameters. The medial condyle is the longer and, when the femur is held with its body perpendicular, projects to a lower level. When, however, the femur is in its natural oblique position the lower surfaces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of the lateral is almost directly antero-posterior, but that of the medial runs backward and medialward. Their opposed surfaces are small, rough, and concave, and form the walls of the intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid line, and below by the central part of the posterior margin of the patellar surface. The

posterior cruciate ligament The posterior cruciate ligament (PCL) is a ligament in each knee of humans and various other animals. It works as a counterpart to the anterior cruciate ligament (ACL). It connects the posterior intercondylar area of the tibia to the medial con ...

of the

joint is attached to the lower and front part of the medial wall of the fossa and the

anterior cruciate ligament The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. The two ligaments are also called "cruciform" ligaments, as they are arranged in a crossed formation ...

to an impression on the upper and back part of its lateral wall. The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the

; it presents a median groove which extends downward to the intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial. Each condyle is surmounted by an elevation, the

epicondyle An epicondyle () is a rounded eminence on a bone that lies upon a condyle ('' epi-'', "upon" + ''condyle'', from a root meaning "knuckle" or "rounded articular area"). There are various epicondyles in the human skeleton, each named by its anatomic ...

. The medial epicondyle is a large convex eminence to which the

tibial collateral ligament The medial collateral ligament (MCL), or tibial collateral ligament (TCL), is one of the four major ligaments of the knee. It is on the medial (inner) side of the knee joint in humans and other primates. Its primary function is to resist outwar ...

of the knee-joint is attached. At its upper part is the

adductor tubercle The adductor tubercle is a tubercle on the lower extremity of the femur. It is formed where the medial lips of the linea aspera The linea aspera ( la, rough line) is a ridge of roughened surface on the posterior surface of the shaft of the fem ...

and behind it is a rough impression which gives origin to the medial head of the

gastrocnemius The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...

. The lateral epicondyle which is smaller and less prominent than the medial, gives attachment to the

fibular collateral ligament The lateral collateral ligament (LCL, long external lateral ligament or fibular collateral ligament) is a ligament located on the lateral (outer) side of the knee, and thus belongs to the extrinsic knee ligaments and posterolateral corner of the k ...

of the

knee-joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the h ...

Development

The femur develops from the

limb bud The limb bud is a structure formed early in vertebrate limb development. As a result of interactions between the ectoderm and underlying mesoderm, formation occurs roughly around the fourth week of development. In the development of the human e ...

s as a result of interactions between the

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...

and the underlying

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Emb ...

, formation occurs roughly around the fourth week of development. Gilbert, Scott F. "Developmental Biology". 9th ed., 2010
/ref> By the sixth week of development, the first

hyaline cartilage Hyaline cartilage is the glass-like (hyaline) and translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-gray in color, with a firm consistency and h ...

model of the femur is formed by

chondrocytes Chondrocytes (, from Greek χόνδρος, ''chondros'' = cartilage + κύτος, ''kytos'' = cell) are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and prote ...

Endochondral ossification Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is produced. Unlike intramembranous ossification, the other process by which bone tissue is produce ...

begins by the end of the

embryonic period Human embryonic development, or human embryogenesis, is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of de ...

and primary

ossification center An ossification center is a point where ossification of the cartilage begins. The first step in ossification is that the cartilage cells at this point enlarge and arrange themselves in rows.Gray and Spitzka (1910), page 44. The matrix in which t ...

s are present in all long bones of the limbs, including the femur, by the 12th week of development. The

development lags behind

forelimb A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial (anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. ...

development by 1–2 days.

Function

As the femur is the only bone in the thigh, it serves as an attachment point for all the muscles that exert their force over the hip and knee joints. Some

biarticular muscle Biarticular muscles are muscles that cross two joints rather than just one, such as the hamstrings which cross both the hip and the knee. The function of these muscles is complex and often depends upon both their anatomy and the activity of othe ...

s – which cross two joints, like the

and

plantaris The plantaris is one of the superficial muscles of the superficial posterior compartment of the leg, one of the fascial compartments of the leg. It is composed of a thin muscle belly and a long thin tendon. While not as thick as the achilles te ...

muscles – also originate from the femur. In all, 23 individual muscles either originate from or insert onto the femur. In cross-section, the thigh is divided up into three separate fascial compartments divided by

fascia A fascia (; plural fasciae or fascias; adjective fascial; from Latin: "band") is a band or sheet of connective tissue, primarily collagen, beneath the skin that attaches to, stabilizes, encloses, and separates muscles and other internal organ ...

, each containing muscles. These compartments use the femur as an axis, and are separated by tough

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tissue ...

membranes (or

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates transit bus, bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people ...

). Each of these compartments has its own

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in th ...

and

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...

supply, and contains a different group of

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

s. These compartments are named the

medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that re ...

and posterior fascial compartments.

Muscle attachments

Clinical significance

Fractures

femoral fracture A femoral fracture is a bone fracture that involves the femur. They are typically sustained in high-impact trauma, such as car crashes, due to the large amount of force needed to break the bone. Fractures of the diaphysis, or middle of the fe ...

that involves the

femoral head The femoral head (femur head or head of the femur) is the highest part of the thigh bone ( femur). It is supported by the femoral neck. Structure The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a ...

femoral neck The femoral neck (femur neck or neck of the femur) is a flattened pyramidal process of bone, connecting the femoral head with the femoral shaft, and forming with the latter a wide angle opening medialward. Structure The neck is flattened from ...

or the

shaft of the femur The body of femur (or shaft of femur) is the almost cylindrical, long part of the femur. It is a little broader above than in the center, broadest and somewhat flattened from before backward below. It is slightly arched, so as to be convex in front ...

immediately below the lesser trochanter may be classified as a

hip fracture A hip fracture is a break that occurs in the upper part of the femur (thigh bone). Symptoms may include pain around the hip, particularly with movement, and shortening of the leg. Usually the person cannot walk. They most often occur as a re ...

, especially when associated with osteoporosis. Femur fractures can be managed in a pre-hospital setting with the use of a

traction splint A traction splint most commonly refers to a splinting device that uses straps attaching over the pelvis or hip as an anchor, a metal rod(s) to mimic normal bone stability and limb length, and a mechanical device to apply traction (used in an at ...

Diversity among animals

Identification-Classification-and-Growth-of-Moa-Chicks-(Aves-Dinornithiformes)-from-the-Genus-pone

In primitive tetrapods, the main points of muscle attachment along the femur are the internal trochanter and third trochanter, and a ridge along the ventral surface of the femoral shaft referred to as the adductor crest. The neck of the femur is generally minimal or absent in the most primitive forms, reflecting a simple attachment to the acetabulum. The greater trochanter was present in the extinct

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avi ...

s, as well as in modern birds and mammals, being associated with the loss of the primitive sprawling gait. The lesser trochanter is a unique development of mammals, which lack both the internal and fourth trochanters. The adductor crest is also often absent in mammals or alternatively reduced to a series of creases along the surface of the bone. Structures analogous to the third trochanter are present in mammals, including some primates. Some species of

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...

, and other non-walking vertebrates have

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

femurs. In some snakes the protruding end of a

pelvic spur Pelvic spurs are the externally visible portion of the vestigial remnants of legs found on each side of the cloaca in primitive snakes, such as boas and pythons. The remnants of a pelvis and femur, which have no connection with the spine, simp ...

, a vestigial pelvis and femur remnant which is not connected to the rest of the skeleton, plays a role in mating. This role in mating is hypothesized to have possibly occurred in ''

Basilosauridae Basilosauridae is a family of extinct cetaceans. They lived during the middle to the early late Eocene and are known from all continents, including Antarctica. They were probably the first fully aquatic cetaceans.Buono M, Fordyce R.E., Marx F. ...

'', an extinct family of whales with well-defined femurs, lower legs and feet. Occasionally, the genes that code for longer extremities cause a modern whale to develop miniature legs (

atavism In biology, an atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations. Atavisms can occur in several ways; one of which is when ...

). One of the earliest known vertebrates to have a femur is the ''

eusthenopteron ''Eusthenopteron'' (from el, εὖ , 'good', el, σθένος , 'strength', and el, πτερόν 'wing' or 'fin') is a genus of prehistoric sarcopterygian (often called lobe-finned fishes) which has attained an iconic status from its clos ...

'', a

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use o ...

lobe-finned fish Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includi ...

from the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

period.

Viral metagenomics

A recent study revealed that bone is a much richer source of persistent DNA viruses than earlier perceived. Besides Parvovirus 19 and hepatitis B virus, ten additional ones were discovered, namely several members of the herpes- and polyomavirus families, as well as human papillomavirus 31 and torque teno virus.

Invertebrates

invertebrate zoology Invertebrate zoology is the subdiscipline of zoology that consists of the study of invertebrates, animals without a backbone (a structure which is found only in fish, amphibians, reptiles, birds and mammals). Invertebrates are a vast and very ...

the name ''femur'' appears in

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

ology. The usage is not homologous with that of vertebrate anatomy; the term "femur" simply has been adopted by analogy and refers, where applicable, to the most proximal of (usually) the two longest jointed segments of the legs of the

arthropoda Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

. The two basal segments preceding the femur are the coxa and trochanter. This convention is not followed in

carcinology Carcinology is a branch of zoology that consists of the study of crustaceans, a group of arthropods that includes lobsters, crayfish, shrimp, krill, copepods, barnacles and crabs. Other names for carcinology are malacostracology, crustaceology, ...

but it applies in

arachnology Arachnology is the scientific study of arachnids, which comprise spiders and related invertebrates such as scorpions, pseudoscorpions, and harvestmen. Those who study spiders and other arachnids are arachnologists. More narrowly, the study of ...

and

entomology Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...

. In

myriapodology Myriapodology is the scientific study of myriapods which includes centipedes and millipedes. The field of myriapodology can also cover other myriapods such as pauropods and symphylans. Those who study myriapods are myriapodologists. Societies * I ...

another segment, the prefemur, connects the trochanter and femur.

Additional media

File:Femur - animation9.gif, Position of human femur (shown in red). Pelvis and

are shown as semi-transparent. File:Fumur Posterior annoted.png, View from behind. File:Fumur Anterior annoted.png, View from the front. File:Human femur.stl, 3D image File:Long Bone (Femur).png, Long bone (femur) File:Slide2DADE.JPG, Muscles of thigh. Lateral view. File:Slide2EA.JPG, Muscles of thigh. Cross section. File:Blausen 0401 Femur DistributionofForces.png, Distribution forces of the femur File:Femur Anatomy by Jason Christian.webm, Femur Anatomy

References

External links

* * * {{Authority control Bones of the lower limb Long bones