In human anatomy, the fibularis tertius (also known as the peroneus tertius) is a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

in the anterior compartment of the leg. It acts to tilt the sole of the foot away from the midline of the body ( eversion) and to pull the foot upward toward the body (

dorsiflexion 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 ...

Structure

The fibularis tertius arises from the lower third of the front surface of 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. ...

, the lower part of the

interosseous membrane An interosseous membrane is a thick dense fibrous sheet of connective tissue that spans the space between two bones, forming a type of syndesmosis joint. Interosseous membranes in the human body: * Interosseous membrane of forearm * Interosseo ...

, and

septum In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...

, or connective tissue, between it and the fibularis brevis. The septum is sometimes called the intermuscular septum of Otto. The muscle passes downward and ends in a tendon that passes under the superior extensor retinaculum and the inferior extensor retinaculum of the foot in the same canal as the

extensor digitorum longus muscle The extensor digitorum longus is a pennate muscle, situated at the lateral part of the front of the leg. Structure It arises from the lateral condyle of the tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, i ...

. It may be mistaken as a fifth tendon of the extensor digitorum longus. The tendon inserts into the medial part of the posterior surface of the shaft of the fifth

metatarsal bone The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...

. The fibularis tertius is supplied by the

deep fibular nerve The deep fibular nerve (also known as deep peroneal nerve) begins at the bifurcation of the common fibular nerve between the fibula and upper part of the fibularis longus, passes infero-medially, deep to the extensor digitorum longus, to the a ...

. In rare cases, it may also be supplied by the common fibular nerve. This is unlike the other fibularis muscles, which are located in the lateral compartment of the leg and are supplied by the

superficial fibular nerve The superficial fibular nerve (also known as superficial peroneal nerve) is a mixed (motor and sensory) nerve that provides motor innervation to the fibularis longus and fibularis brevis muscles, and sensory innervation to skin over the antero- ...

, since the fibularis tertius is found in the anterior compartment of the leg. The fibularis tertius may be absent in

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

. It may be absent in as few as 5% of people, or as many as 72%, depending on the population surveyed. It is rarely found in other

primates Primates is an order of mammals, which is further divided into the strepsirrhines, which include lemurs, galagos, and lorisids; and the haplorhines, which include tarsiers and simians ( monkeys and apes). Primates arose 74–63 ...

, which is one reason its function has been linked to efficient

bipedalism Bipedalism is a form of terrestrial locomotion where an animal moves by means of its two rear (or lower) Limb (anatomy), limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from ...

Function

As a weak dorsiflexor of the ankle joint, the fibularis tertius assists in pulling the foot upward toward the body. It also assists in tilting the sole of the foot away from midline of the body at the ankle ( eversion). It is likely to be helpful though not essential in bipedal walking.

Clinical significance

The fibularis tertius may be involved in ankle injuries and may rupture. This is caused by hyperextension. The fibularis tertius may be imaged using

medical ultrasound Medical ultrasound includes Medical diagnosis, diagnostic techniques (mainly medical imaging, imaging) using ultrasound, as well as therapeutic ultrasound, therapeutic applications of ultrasound. In diagnosis, it is used to create an image of ...

Nomenclature and etymology

Terminologia Anatomica ''Terminologia Anatomica'' (commonly abbreviated TA) is the international standard for human anatomy, human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology (FIPAT) a program of the Inter ...

'' designates "fibularis" as the preferred word over "peroneus.". The word "peroneus" comes from the Greek word "perone," meaning pin of a brooch or a buckle. In medical terminology, the word refers to being of or relating to the fibula or to the outer portion of the leg.

Other animals

The fibularis tertius muscle in

horses The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 milli ...

originates from the near the lateral condyle of the femur, passes through the extensor sulcus on the head 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 inserts onto the third

, the third and fourth tarsal bones, and the

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 ...

. Rupture of the muscle may cause 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 ...

to have a slight dip.

Additional images

File:Peroneus tertius.png, Muscles of the front of the leg (fibularis tertius visible at center left). File:Gray268.png, Bones of the right foot (dorsal surface). File:Gray441.png, The mucous sheaths of the tendons around the ankle (lateral aspect). File:Slide1ABBAA.JPG, Dorsum of foot. Deep dissection. File:Slide2ABBAA.JPG, Dorsum of foot. Deep dissection.

References

External links

* - "The Leg: Muscles"
PTCentral
{{Authority control Muscles of the lower limb