Transcript

Anatomy of the leg

From Osmosis from Elsevier · Episode page · Watch on YouTube

· 23 min · 3,247 words · 29 timestamped sections

This is the full, timestamped transcript of "Anatomy of the leg", an episode of Osmosis from Elsevier published December 21, 2025 (23 min, about 3,247 words). It mentions 19 people, works and ideas, including tibialis anterior, anterior tibial artery, fibularis longus, tibial nerve, tibialis posterior.

What is discussed, and when

  1. – 5:00: tibialis anterior, extensor digitorum longus, anterior tibial artery, deep fibular nerve
  2. – 10:00: fibularis longus, anterior tibial artery, fibularis brevis, tibialis anterior
  3. – 15:00: anterior tibial artery, fibular artery, flexor digitorum longus, plantaris
  4. – 20:00: tibial nerve, tibialis posterior, flexor digitorum longus, fibular artery
  5. – 23:07: fibular artery, fibularis brevis, fibularis longus, flexor digitorum longus

Notable quotes from "Anatomy of the leg"

  • Dense, providing part of the proximal attachment of the muscle immediately deep to it, the tibialis anterior.
    about tibialis anterior · at
  • The muscles in the anterior compartment are inervated by the deep fibular nerve and blood is supplied via the anterior tibial artery.
    about anterior tibial artery · at
  • Nerve. It's one of the two terminal branches of the common fibular nerve arising between the fibularis longus muscle and the neck of the fibula. After its entry into the…
    about fibularis longus · at
  • The fibularis brevis lies deep to the fibularis longus and it's the shorter of the two. It originates on the inferior 2/3 of the lateral surface of the fibula and its fibers converge to form a tendon.
    about fibularis brevis · at
  • Accompanying veins penetrate the anterior interuscular septum. Distally, perforating branches of the fibular artery and accompanying veins penetrate the posterior interuscular septum.
    about fibular artery · at
  • Posterior compartment are collectively called the calf muscles namely the gastronmus, solius and plantaris.
    about plantaris · at
  • Fun fact, this tendonous arch of the soius is where the poplidial artery and the tibial nerve exit the poplidial fossa. It's also where the poplidial artery bifurcates into its…
    about tibial nerve · at
  • Posterior compartment, namely the poplitius, flexor digitorum longus, flexoralis longus, and tibialis posterior.
    about tibialis posterior · at

Who and what is mentioned in this episode?

Companies & orgs

  • Osmosis — Company · 1 mention · first at
    Septum and the medial surface of the fibula. Enjoying our Osmosis videos?

Concepts & topics

Full transcript with timestamps

The leg is the region of the lower limb between the knee and the ankle. It's a tightly packed region consisting of muscles and neurovvascular structures. The leg is organized into three fascial compartments. An anterior, lateral, and posterior which are formed by the interosius membrane, the anterior intramuscular septum and the posterior intramuscular septum. The anterior compartment of the leg is also known as the extensor or dorsif flexor compartment, and it's the area of the body you use to locate furniture after you turn off the lights. Ouch.

It's bound anteriorly by the deep fascia of the leg and skin, posteriorly by the interosius membrane, medially by the lateral surface of the tibia, and laterally by the anterior intramuscular septum and the medial surface of the fibula. Enjoying our Osmosis videos? Unlock your full potential with an Osmosis subscription. Get unlimited access to every Osmosis feature and resource with a free 7-day trial. Now, proximally, the deep fascia overlying the anterior compartment is dense, providing part of the proximal attachment of the muscle immediately deep to it, the tibialis anterior.

Distally, the deep fascia presents two band-like thickenings organized as two retininocula. Retininocula help secure and provide leverage for the tendons of the anterior compartment muscles before and after they cross the ankle joint. Specifically, the retininocula prevent these tendons from bow stringing anteriorly during movement of the joint. First, there's the superior extensor retininoculum, which is a strong broad band of deep fascia passing from the fibula to the tibia proximal to the maloli. Second, there's the inferior extensor retininoculum, a Y-shaped band of deep fascia that attaches laterally to the antrouperior surface of the calccanous and medially to the medial malololis and medial ununiform. It forms a strong loop around the tendons of the fibularis tertiius and the extensor digitorum longus muscles.

The anterior compartment contains four muscles. The tibialis anterior extensor digtorum longus extensor halysis longus and fibularis tertiius which are all dorsif flexors of the ankle raising the toes and depressing the heel. To remember dorsif flexion, think of the phrase fins to shins with your toes being the fins you use to swim and you're bringing them up to your shins. The muscles in the anterior compartment are inervated by the deep fibular nerve and blood is supplied via the anterior tibial artery. The tibialis anterior is the most medial and superficial dorsif flexor and it lies against the lateral surface of the tibia. It originates on the lateral condile in the superior half of the lateral surface of the tibia and the interosius membrane.

About halfway down the leg, its muscular fibers are replaced by the muscle's tendon, which continues its descent along the anterior surface of the tibia. It passes deep to the superior and inferior extensor retininocula and inserts to the medial and inferior surfaces of the medial ununiform and the base of the first metatarsal. The tibialis anterior is the strongest dorsif flexor of the ankle and it also helps produce inversion or turning of the sole of the foot inwards. Second, the extensor digorum longus is the most lateral of the anterior leg muscles. Its origin is at the lateral condile of the tibia and the superior 3/arters of the medial surface of the fibula and interosius membrane. The extensor digtorum longus forms four tendons superior to the ankle which enter the dorsome of the foot along with the tendon of the closely associated fibularis tertiius muscle. Once the tendons reach the fanges they divide

into two lateral bands and one central band. The central band inserts into the base of the middle phalank and the lateral bands converge to insert into the base of the distal falank. The extensor digitorum longus extends the lateral four digits and dorsif flexes the ankle. Third, the extensor halysis longus is a thin muscle that lies deeply between the tibialis anterior and extensor digtorum longus. Its origin is the middle part of the anterior surface of the fibula and interosius membrane. The muscle courses distally along the crest of the dorsom of the foot to the great toe and it inserts on the dorsal aspect of the base of the distal falank of the great toe.

The muscle extends to the great toe and unsurprisingly also dorsiflexes the ankle. And finally the fibularis terteius which proximally originates on the inferior third of the anterior surface of the fibula and interosius membrane and inserts on the dorsome of the fifth metatarsal. The fibularis tertiius dorsal flexes the ankle and it also participates in everversion of the ankle or turning the sole of the foot outwards. Now let's talk about the neurovvascular structures in the anterior compartment of the leg. The main nerve of the anterior compartment is the deep fibular nerve. It's one of the two terminal branches of the common fibular nerve arising between the fibularis longus muscle and the neck of the fibula. After its entry into the anterior compartment, the deep fibular nerve accompanies the anterior tibial artery. First between the tibialis anterior and extensor digitorum longus and then between the

tibialis anterior and extensor halysis longus. It then exits the compartment at the distal end of the tibia and enters the dorsome of the foot. Now along its way it sends motor branches to the anterior muscles of the leg and dorsom of the foot. Finally it provides sensory intervation to the skin of the first interdigital cleft which is the skin between the first and the second toe as well as to the joints it crosses via articular branches. Finally, the anterior compartment is mainly supplied by the anterior tibial artery, which is the smaller terminal branch of the poplidial artery. The anterior tibial artery begins at the inferior border of the poplitius muscle and immediately passes anteriorly through a gap in the superior part of the interosius membrane which it descends on its anterior surface between the tibialis anterior and extensor digitorum muscles. At the ankle joint midway between the maloli the anterior

tibial artery changes names becoming the dorsalis pedus artery. Well, that was, shall I say, legendary. How about a quick break to see if you can recognize the main structures of the anterior compartment of the leg. Moving on to the lateral compartment of the leg or the compartment. This space is bound medially by the lateral surface of the fibula, laterally by deep fascia of the leg, anteriorly by the anterior intramuscular septum and posteriorly by the posterior intramuscular septum. From its superior limit at the level of the poplidial fossa, the lateral compartment ends inferiorly at the superior fibular retininoculum.

The lateral compartment contains two fibularis muscles, longus and brevis. The fibularis longus, as its name suggests, is the longer and more superficial of the two fibularis muscles. It originates on the head and superior 2/3 of the lateral surface of the fibula. From this point, it travels distally behind the lateral malololis and deep to the inferior fibular retinacculum. It eventually enters a groove on the antro inferior aspect of the cuboid as it crosses the sole of the foot running obliquely and distally to reach its insertion on the base of the first metatarsal and medial ununiform bones.

The fibularis brevis lies deep to the fibularis longus and it's the shorter of the two. It originates on the inferior 2/3 of the lateral surface of the fibula and its fibers converge to form a tendon which passes posterior to the lateral malololis. It passes anteriorly and laterally to insert on the dorsal surface of the tuberosity of the fifth metatarsal. The fibularis brevis helps maintain the lateral longitudinal arch of the foot. Both fibularis muscles help with everversion and contribute to weak planter flexion at the ankle.

The superficial fibular nerve which is the other terminal branch of the common fibular nerve intervates the lateral compartment. It arises between the most proximal attachment of the fibularis longus and the neck of the fibula from where it descends down the leg until it pierces the deep fascia at the distal third of the leg to become subcutaneous. Now the superficial fibular nerve supplies motor intervation to the fibularis muscles and sensory intervation to the skin on the distal part of the anterior surface of the leg and nearly all of the dorsom of the foot.

When it comes to arteries and veins, the lateral compartment does not have a major blood vessel coursing through it. Instead, perforating branches and accompanying veins supply blood to and drain blood from the lateral compartment. Proximally, perforating branches of the anterior tibial artery and their accompanying veins penetrate the anterior interuscular septum. Distally, perforating branches of the fibular artery and accompanying veins penetrate the posterior interuscular septum. Now, that was a lot of info. Let's take a break now and try to recognize the components of the lateral compartment of the leg.

And finally, we've reached the posterior compartment of the leg or the planter flexor compartment, which is the largest of the three. Now, the posterior compartment is divided into a superficial and a deep subcompartment by the transverse interuscular septum. The superficial subcompartment is larger and its borders are the transverse intramuscular septum anteriorly and the skin posteriorly while the deep subcompartment is smaller and sits posterior to the tibia fibula and the interosius membrane. Inferiorly, the deep subcompartment tapers and becomes smaller distally and the distal transverse interuscular septum fibers extend between the tip of the medial malololis and the calccanous as the flexor retininoculum.

This retininoculum creates a compartment for the tendons and neurovvascular structures of the posterior compartment to enter the foot behind the medial malololis which is often referred to as the tarsel tunnel. So the muscles of the superficial posterior compartment are collectively called the calf muscles namely the gastronmus, solius and plantaris. Collectively the gastronmus and solius make up the three-headed triceps suri while the plantaras is a small muscle with a short belly and a long tendon that may be absent in up to 10% of people. The superficial muscles form the characteristic calf shape of the posterior leg and they all insert into the calccanous of the foot via the calccanial tendon.

The gastronmius is the most superficial muscle in the posterior compartment and forms the proximal and most prominent part of the calf. It has a medial head which originates from the poplidial surface of the femur superior to the medial femoral condile and a lateral head which originates from the lateral aspect of the lateral femoral condile. As the muscle descends its fibers converge at the inferior margin of the poplidial fossa for which they form the infrateral border and infromedial border. Distally, the belly of the gastronmus combines with the solius to form the calccanial tendon, better known as the Achilles tendon, which inserts into the posterior surface of the calccanous. The gastronmus is a major planter flexor of the ankle, and since it also crosses the knee joint, it flexes the knee as well.

Next, there's the solius, which is deep to the gastronmus. It's a large muscle named with a proximal attachment in the shape of an inverted U. Specifically, it originates on the posterior aspect of the head of the fibula and posterior surface of the fibula, the solio line of the tibia and the tendonous arch extending between these two bony attachments. Fun fact, this tendonous arch of the soius is where the poplidial artery and the tibial nerve exit the poplidial fossa. It's also where the poplidial artery bifurcates into its terminal branches, the anterior and posterior tibial arteries. So there's a lot going on there.

When the knee is extended, the soius acts with the gastronmus and causes planter flexion of the ankle. When the knee is flexed, the gastronmus is not in tension and the soius causes planter flexion all by itself. So long story short, if you want to work out your gastronmus muscles, do standing calf raises. And if you want to work out your solius muscles underneath, do seated calf raises. And finally, the planter originates from the lateral supracondular line of the femur and the oblique poplidial ligament, descends medially, and condenses into a tendon that runs down the leg between the gastronmus and solius. And just like its two much larger brothers, its tendon blends with the calccanial tendon. This mysterious muscle acts in tandem with the gastronmus. But due to its size, its function outside of proprioception is insignificant.

And now for the four deep muscles of the posterior compartment, namely the poplitius, flexor digitorum longus, flexoralis longus, and tibialis posterior. First the poplitius is a thin triangular muscle that forms the inferior part of the floor of the poplidial fausa. It originates on the lateral aspect of the lateral femoral condile and the posterior horn of the lateral meniscus. From there it runs infromedially towards the tibia and inserts on the posterior surface of the tibia above the solio line. The poplitius unlocks the locked knee from a standing position to a flexed position by rotating the femur laterally during initial stages of flexion of the knee.

Next, flexor halysis longus originates from the posterior surface of the inferior two/3s of the fibula and inferior part of the interosius membrane descends inferiorly from the posterol lateral to the postermed medial side of the leg and passes posterior to the medial malololis towards the sole of the foot. Ultimately, it inserts at the base of the distal falank of the great toe. The flexor halysis longus muscle flexes all of the joints of the great toe in addition to weak planter flexion of the ankle. Third, the flexor digitorum longus is smaller than the other flexors. It originates from the medial part of the posterior surface of the tibia inferior to the solio line and descends the medial aspect of the posterior leg. It then passes diagonally posterior to the medial malololis into the sole of the foot crossing the tendon of the flexoralis longus superficially on its way. After it crosses the flexoralis

longus tendon the flexor digitorum longus divides into four tendons and inserts into the base of the distal fanges of the lateral four digits. This muscle flexes the lateral four digits and helps with planter flexion of the ankle. And finally the tibialis posterior is the deepest muscle in the posterior compartment and it lies between the two flexors in the same plane as the tibia and fibula. It originates from the interosius membrane and the adjacent posterior surfaces of the tibia and fibula and it descends down the leg between the two muscles until it passes posterior to the medial malololis and reaches the calccanous deep to the two flexor tendons. The tibialis posterior inserts into the tuberosity of the novicular bone ununiforms cuboid and sustentaculum tali of the calccanous along with the bases of the second, third and fourth metatarscils.

Its main job is to work with the tibialis anterior to produce inversion and it also helps with planter flexion of the ankle. Finally, it also supports or maintains the medial longitudinal arch of the foot during weightbearing. You've probably noticed a common theme to these three deep subcompartment muscles as they enter the foot, and that is that they pass posterior to the medial malololis in what is called the toarsel tunnel. This is a great anatomical landmark to help distinguish the muscular tendons and neurovvascular structures of the posterior compartment as they travel into the foot. From anterior to posterior the structures can be identified using the pneummonic tom dick and nervous hairy. The first and most anterior structure passing behind the medial malololis is the tibialis posterior. Then the flexor digtorum longus followed by the posterior tibial artery. Then the tibial nerve and

finally the flexor halysis longus. Speaking of nerves, the tibial nerve is the most important as it intervates all the muscles in the posterior compartment. The tibial nerve is the larger of the two terminal branches of the sciatic nerve. It runs vertically through the poplidial fossa with the poplidial artery passing between the heads of the gastronmus deep to the tendonous arch of the soius. At the ankle, the nerve lies between the tendons of the flexor halysis longus and flexor digtorum longus. And after traveling deep to the flexor retininoculum, the tibial nerve divides into the medial and lateral planter nerves.

Switching to arteries, the posterior tibial artery provides the blood supply to the posterior compartment of the leg and the foot. It's the larger and more direct terminal branch of the poplidial artery. It begins at the distal border of the poplitius as the poplidial artery passes deep to the tendonous arch of the soius and simultaneously bifrocates into the anterior and posterior tibial arteries. The posterior tibial artery is accompanied by the tibial nerve and veins and it runs posterior to the medial malololis as described previously. Deep to the flexor retininoculum, the posterior tibial artery divides into medial and lateral planter arteries, the arteries of the sole of the foot.

Finally, there's the fibular artery. The largest and most important branch of the posterior tibial artery. It arises inferior to the distal border of the poplitius and the tendonous arch of the soius and it descends obliquely toward the fibula running down the medial side of the fibula parallel to the posterior tibial artery within the deep compartment. The fibular artery gives rise to the nutrient artery of the fibula, the largest nutrient artery in the body. It also gives off numerous muscular branches to both the posterior compartment and lateral compartment of the leg. Distally, the fibular artery also contributes branches to the perarticular anastmosis of the ankle.

Okay, fantastic job. You've made it till the end. Before we recap, let's see if you can remember the components of the posterior compartment of the leg. All right, as a quick recap, the leg is organized into three fascial compartments. The anterior compartment is bound posteriorly by the interosius membrane, medially by the tibia, and laterally by the fibula and anterior intramuscular septum. Anteriorly, it's bound by the deep fascia of the leg and skin. Inferiorly, the deep fascia forms the superior extensor retininoculum and the inferior extensor retininoculum. The anterior compartment contains the muscles tibialis anterior, the extensor digtorm longus, the extensor halysis longus and the fibularis tertiius.

The lateral compartment of the leg contains the muscles fibularis longus and fibularis brevis which are responsible for everversion of the foot and planter flexion at the ankle. The posterior compartment of the leg is divided into a superficial and deep subcompartment by the transverse interuscular septum. The superficial muscles are the gastronmus, solius and plantaris. They all produce the action of planter flexion at the ankle. These muscles also form the calf shape of the posterior leg and they all insert into the calccanous of the foot via the calccanial or achilles tendon.

The deep muscles are represented by the poplidius flexor digitorum longus flexor halysis longus and tibialis posterior. To remember the structures of the posterior compartment passing posterior to the medial malololis, we can use the pneummonic tom dick and nervous hairy representing from anterior to posterior the tibialis posterior flexor digitorum longus the posterior tibial artery the tibial nerve and the flexoralysis longus.

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Questions about this episode

What is discussed in "Anatomy of the leg"?

In order: 0:00 tibialis anterior, extensor digitorum longus, anterior tibial artery, deep fibular nerve; 5:00 fibularis longus, anterior tibial artery, fibularis brevis, tibialis anterior; 10:00 anterior tibial artery, fibular artery, flexor digitorum longus, plantaris; 15:00 tibial nerve, tibialis posterior, flexor digitorum longus, fibular artery; 20:00 fibular artery, fibularis brevis, fibularis longus, flexor digitorum longus.

What is mentioned in this Osmosis from Elsevier episode?

19 people, works and ideas are mentioned, including tibialis anterior, anterior tibial artery, fibularis longus, tibial nerve, tibialis posterior, flexor digitorum longus. Each one on this page links to its own page with every episode that mentions it.

How long is "Anatomy of the leg"?

The episode runs 23 min; the transcript is about 3,247 words in 29 timestamped sections.

More from Osmosis from Elsevier

About this transcript: the episode's spoken words as captioned on YouTube, split into timestamped sections. Reclip.Me locates every person, work and idea in the text, keeps the time it is first named, and quotes the words around it verbatim. Last updated January 12, 2026.