In human anatomy, the fibularis tertius (also known as the peroneus tertius) is a muscle 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 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. Its upper extremity i ...

, 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 * Interosseou ...

, and septum, or connective tissue, between it and the

fibularis brevis In human anatomy, the fibularis brevis (or peroneus brevis) is a muscle that lies underneath the fibularis longus within the lateral compartment of the leg. It acts to tilt the sole of the foot away from the midline of the body (eversion) and to e ...

. 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. 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, 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 ...

. 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 anter ...

. In rare cases, it may also be supplied by the

common fibular nerve The common fibular nerve (also known as the common peroneal nerve, external popliteal nerve, or lateral popliteal nerve) is a nerve in the lower leg that provides sensation over the posterolateral part of the leg and the knee joint. It divides at ...

. This is unlike the other

fibularis muscles The fibularis muscles (also called peroneus muscles or peroneals) are a group of muscles in the lower leg. Description The muscle group is normally composed of three muscles: fibularis longus, fibularis brevis, and fibularis tertius. The fib ...

, which are located in the

lateral compartment of the leg The lateral compartment of the leg is a fascial compartment of the lower leg. It contains muscles which make eversion and plantarflexion of the foot. Muscles The lateral compartment of the leg contains: * Fibularis longus * Fibularis brevis ...

and are supplied by the superficial fibular nerve, since the fibularis tertius is found in the anterior compartment of the leg. The fibularis tertius may be absent in

humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

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

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

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 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 ...

. The fibularis tertius may be imaged using

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

Nomenclature and etymology

Terminologia Anatomica ''Terminologia Anatomica'' is the international standard for human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology, a program of the International Federation of Associations of Anatomi ...

'' 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 originates from the near the lateral condyle of the femur, passes through the extensor sulcus on the head of 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 ...

, and inserts onto the third

, the third and fourth

tarsal bones In the human body, the tarsus is a cluster of seven articulating bones in each foot situated between the lower end of the tibia and the fibula of the lower leg and the metatarsus. It is made up of the midfoot ( cuboid, medial, intermediate, and ...

, and the calcaneus. 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 calcaneus ( ...

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