In this video I want to talk about the muscles of the leg.
Remember when we did the arm we had an anterior and a posterior compartment.
And when we did the thigh we had anterior posterior and a medial compartment.
In the forearm we had an anterior and a posterior compartment.
In the leg, remember from the knee to the ankle, we are going to have an anterior and
a posterior and a lateral compartment.
Let's first take a look at the anterior compartment of the leg.
Remember the large bone in the leg, the weight-bearing bone, was the tibia.
And it was a subcutaneous bone.
We can feel it under the skin because really there is no muscle covering over the anterior
tibia.
The muscle is actually lateral to the tibia.
So in this diagram we can see that the most anterior muscle in this region is known as
the tibialis anterior.
And on this model we can see it running down anterior to the ankle and out onto the medial
aspect of the dorsum of the foot.
This makes the tibialis anterior an inverter and a dorsiflexor of the foot.
Remember dorsiflexion is pointing the foot up towards the sky.
Inversion is turning the sole of the foot up inward.
So tibialis anterior, a dorsiflexor and inverter of the foot.
Next to the tibialis anterior we can see the muscle known as the extensor digitorum longus.
Now keep in mind in the forearm we had an extensor digitorum.
In the leg we are going to have an extensor digitorum longus.
That tells us we will also see an extensor digitorum brevis.
Not yet.
So here's our extensor digitorum longus.
And it splits into 4 tendons going to digits 2, 3, 4, and 5.
So the extensor digitorum longus to digits 2, 3, 4, and 5.
Extends toes 2, 3, 4, 5.
Also splitting away from the extensor digitorum longus there's a third muscle called the peroneus
tertius.
Peroneus tertius appears to be heading toward the digits but it actually goes to the lateral
aspect of the foot.
So this peroneus tertius acts as a dorsiflexor of the foot and an everter of the foot.
It is going to lift the lateral side of the foot, which would be turning the sole away
from midline.
So far we have seen three muscles in the anterior leg.
Tibialis anterior, extensor digitorum longus, and splitting away from that, low here, the
peroneus tertius.
There is a fourth muscle in the anterior leg.
That muscle is the extensor hallucis longus.
The hallux is the big toe.
If we look deep between tibialis anterior and extensor digitorum longus we will see
another muscle coming down and breaking off into a tendon, and the tendon goes only to
the big toe on the dorsum of the foot.
The extensor digitorum longus.
If we look at the lateral aspect of this leg, and I'm going to remove the muscles of the
anterior compartment so we can have no confusion, we will see two muscles, the peroneus longus
and the peroneus brevis.
Remember we have already seen a peroneus tertius.
The peroneus longus has origin off of the upper two thirds of the lateral aspect of
the fibula.
Whereas the peroneus brevis has origin off of the lower lateral two thirds of the fibula.
So there is a one third overlap in the middle.
So this upper portion is peroneus longus, the lower portion is peroneus brevis.
It is the insertion that is going to be of importance.
Peroneus longus makes a tendon that will go posterior to the lateral malleolus of the
ankle and then disappear under the foot, where it travels all the way across the bottom of
the foot to insert on the medial side of the foot.
Because it goes posterior to the lateral malleolus it is going to be a plantar flexor of the
foot.
And because it will pull down on the medial aspect of the foot, it will be an everter
of the foot.
Now the lower portion of this forms the peroneus brevis.
Peroneus brevis turns and its tendon inserts on the lateral aspect of the foot.
But it did pass posterior to the lateral malleolus of the foot to reach that lateral aspect.
So peroneus brevis is also a plantar flexor of the foot, but it lifts the lateral aspect
of the foot, which would be eversion.
So it is an everter of the foot.
So we have the peroneus longus and peroneus brevis in the lateral compartment of the leg.
They were both everters of the foot.
They are both plantar flexors of the foot.
Now if we add back in our peroneus tertius from the anterior compartment of the leg,
we have a peroneus longus, a peroneus brevis, and a peroneus tertius.
All of them are everters of the foot.
But peroneus longus and brevis, because they went behind the lateral malleolus, are plantar
flexors of the foot.
Whereas peroneus tertius was a dorsiflexor of the foot.