If we now move on to the posterior compartment of the leg, we can see we have both superficial
and deep layers that I mentioned. Let’s deal with the superficial layers first.
On here, we can see most superficially closest to the skin, we have gastrocnemius. And this
has two heads. There’s a lateral head to gastrocnemius we can see running over here.
This is a lateral head of gastrocnemius, and here we can see the medial head of gastrocnemius.
So here, we have the posterior view of a right leg. We have the lateral head of gastrocnemius
here, and we have the medial head here. Deep to gastrocnemius, we find we have soleus,
and this is a large muscle, a very fleshy muscle that is sitting directly deep to gastrocnemius.
So gastrocnemius, the lateral head, comes from the lateral condyle of the femur while
the medial head comes from the medial condyle of the femur. Soleus, this comes from the
posterior surface of the fibula, and also as we mentioned in the osteology lecture,
it comes from the soleal line of the tibia. Both of these muscles pass through the posterior
aspect of the calcaneus via the calcaneal tendon. They’re supplied by the tibial nerve.
So these muscles in the posterior compartment are supplied by the tibial nerve, one of those
divisions that are coming away from the sciatic nerve. Gastrocnemius and soleus are both involved
in plantarflexion of the ankle, so enabling you to stand on tiptoes. And because gastrocnemius
crosses the knee joints, then it can actually flex the knee as well. One other muscle that
I haven’t mentioned is plantaris. Plantaris is running alongside the medial aspect of
the lateral head, and this gives rise to a very thin and long tendon that runs between
gastrocnemius and soleus. So we can see plantaris. It’s coming from the inferior aspect of
the lateral supracondylar ridge of the femur, and its long tendon passes between the soleus
muscle and the gastrocnemius muscle. It has a long tendon that then blends with the calcaneal
tendon inserting on to the calcaneus. It’s in the posterior compartment. So it’s also
supplied by the tibial nerve, and it is a weak plantarflexor of the ankle. If we look
at more deep layers, then there are three muscles here that I want to talk about, first
of all. We have popliteus, flexor digitorum longus, and flexor hallucis longus.
So we can see these if we look into the deep compartments. We have popliteus here.
We have flexor digitorum longus. We have flexor hallucis longus.
So popliteus, we can see coming from these
lateral aspects of the leg. It’s coming from the lateral surface of the femoral condyle.
We can see it’s passing across to the tibia. We then have long muscles that give rise to
tendons that pass into the foot, flexor digitorum longus and flexor hallucis longus. So we can
see popliteus coming from the lateral aspects of the lateral condyle of the femur. It also
comes from the lateral meniscus, and it passes to the posterior tibia above the soleal line
which we mentioned before. Flexor digitorum longus, this is coming from the posterior
surface of the tibia below the soleal line, and this passes to the distal phalanges of
digits 2 to 5. Flexor hallucis longus, this is coming from the lower two-thirds of the
posterior fibula, and also their interosseous membrane. It passes to the distal phalanx
of the great toe. All of these muscles, as they’re in the posterior compartment, are
supplied by the tibial nerve. Popliteus, this is going to be a weak knee flexor.
It’s also involved in unlocking the knee by lateral rotation of the femur on a stable tibia.
So when you’re in standing position and the femoral condyle is tightly articulating with
the tibial plateau, then popliteus is important in unlocking the knee enabling flexion to occur.
Flexor digitorum longus flexes the digits 2 to 5, and it also helps to plantarflex
the ankle. Flexor hallucis longus flexes the great toe and is also a weak plantarflexor.
There’s a fourth muscle in the deep layer of the posterior compartment of the leg.
That is the Tibialis posterior. It originates as 2 bands on the posterior surface of the tibia,
fibula, and interosseous membrane and then merges into 1 muscle mass half-way down the leg.
At the ankle, the tibialis posterior passes between the medial malleolus of the tibia
and continues on the medial side of the foot, passing under the flexor retinaculum.
In the foot, the tibialis posterior inserts into the tuberosity of the navicular bone,
medial cuneiform bone, and the bases of the second, third, and fourth metatarsal bones.
This muscle is the main invertor of the foot and also aids in plantarflexion as well as
supporting the plantar arches.