Okay so this is the second tutorial on the muscles of the leg, so in this tutorial I'm
going to cover the muscles of the anterior and lateral compartments.
So these compartments are supplied by the common peroneal branch of the sciatic nerve.
So the sciatic nerve splits into two branches at the popliteal fossa.
The tibial branch supplies the posterior compartment, and then you've got the common fibular, or
common peroneal branch, which winds round laterally, over the head of the...the lateral
head of the gastrocnemius, over the neck of the fibula, where it's vulnerable to impact
injuries and fractures, and then it splits into two branches which supply the anterior
and the lateral compartments.
So I'll just fade away the muscles and then you can see how this nerve splits.
So you've got the common fibular branch coming around laterally, and then it splits into
these two branches: you've got the superficial branch, which supplies the muscles of the
lateral compartment, and you've got the deep branch, which supplies the anterior compartment.
So the muscles of the anterior compartment mainly act to dorsiflex, extend to the toes,
and to invert the foot, and there are four muscles in this compartment, and this compartment
is supplied by the deep branch of the common fibular nerve.
The lateral compartment only has two muscles, and these muscles mainly act to evert the
foot.
And this compartment is supplied by the superficial branch of the common fibular nerve.
Okay so you have two muscles in the lateral compartment of the leg, you've got the peroneus
longus, or the fibularis longus, which is this muscle here.
And you've got the fibularis brevis, which lies deep to the fibularis longus, and it
attaches a bit lower down on the fibula.
So I'll just show you the fibularis longus muscle.
So the fibularis longus muscle, as you can see its origin, attaches on the upper lateral
surface of the fibula, and also on the lateral side of the head of the fibula, and it has
an interesting tendon, because it actually crosses over underneath the foot to insert
medially at the distal end of the medial cuneiform bone, and at the base of the proximal, sorry,
the base of the first metatarsal here.
So if we just follow this tendon round, you can see it runs down behind the lateral malleolus
and then it descends and curves forwards on the lateral side of the calcaneus and then
passes under the foot.
And it then passes under the cuboid bone, and in this bone there's a groove for the...for
the tendon.
So I'll just show you that.
So if we just look, I've just rotated the model and we're looking at the underside of
the foot - the plantar surface of the foot, so this is the cuboid bone, which is one of
the tarsal bones that sits laterally.
So the tendon of the peroneus longus actually runs in a groove in this cuboid bone.
I think it's a little bit out of place here, but you can see this groove here, so the tendon
runs underneath the foot, through the groove on the cuboid bone and attaches to the base...base
of the first metatarsal and also distally on the medial cuneiform bone.
So you can just see that tendon coming across, and it inserts distally on the medial cuneiform,
and at the base of this first metatarsal.
So what this muscle does is that it actually everts the foot and it can also assist in
plantarflexion.
So you can just imagine, so seeing the insertion point here, you could just visualise if this
muscle were to contract it would pull this, pull the foot round into eversion.
So eversion is when the soles of the feet face away from each other, and inversion is
when you bring the soles of the feet to face each other.
So another point about the peroneus longus is that it actually provides support for the
arches of the foot.
So it mainly supports the lateral and transverse arches, and if you remember in my last tutorial,
the tibialis posterior also provided support to the arch, due to its insertion on the medial
aspect of the foot, and there's another muscle which I'll come on to talk about later in
this tutorial, called the tibialis anterior, which also inserts medially on the foot, and
contributes to arch support.
So I've just brought back in all the muscles, and this muscle here is the tibialis anterior,
which I'll talk about later, and you can see its tendon which winds round and inserts also
on the base of the first metatarsal.
And if I just remove this muscle here, you can see the tibialis posterior tendon.
So you've got these three tendons coming in to attach to the underside on the medial aspect
of the foot, and these sort of act to support the arches.
So you've got the tibialis anterior tendon here, you've got the tibialis posterior tendon,
and you've got the peroneus longus tendon, or the fibularis longus tendon coming in from
this side.
So these all function to support the arches of the foot.
So next we've got the peroneus brevis muscle, the fibularis brevis, so if we just remove
the...this muscle.
So this lies deep to the fibularis longus, and this lies on the lower two thirds, on
the lateral surface of the shaft of the fibula, and you can see this tendon here, it winds
round behind the lateral malleolus, just like the fibularis longus, and it curves round
and inserts onto the base of the fifth metatarsal.
So what this muscle does is it everts the foot.
So the peroneus brevis and peroneus longus, or fibularis brevis/fibularis longus if you
want, are innervated by the superficial branch of the common peroneal or common fibular nerve.
So next we've got the muscles of the anterior compartment of the leg, and there are four
muscles in this compartment, you've got the tibialis anterior, the extensor hallucis longus,
the extensor digitorum longus, and the fibularis tertius.
So these muscles mainly act to dorsiflex, extend the toes, and to invert the foot.
So I'll start with this muscle here, the tibialis anterior, which is the most superficial muscle.
So I've just isolated this muscle and you can see its attachment on the tibia, on the
lateral side of the tibia, and on the adjacent interosseus membrane.
So this muscle forms a tendon which runs down the front of the leg and inserts medially
on the foot.
So this, this muscle actually provides support for the arch of the foot, as well as the tibialis
posterior and the fibularis longus.
So you can see its attachment on the foot here, so it inserts on the medial, the sort
of lower surface of the medial cuneiform bone and on the adjacent base of the first metatarsal.
So you can see by this medial attachment on the foot, that if this muscle contracts, it
would pull the foot up, so that it will invert the foot, so again inversion is when you bring
the foot up so both the soles face each other.
And it will also dorsiflex the foot, so it will pull the...pull the toes up in this direction
towards the head.
So that's the tibialis anterior, and it's innervated by the deep branch of the common
peroneal nerve, so the deep, or the fibular nerve, the deep fibular nerve - so all the
muscles in the anterior compartment are innervated by the deep fibular nerve.
So next we've got the two extensor muscles of the digits and of the great toe.
So you've got the extensor digitorum longus, and the extensor hallucis longus.
So just like in the posterior compartment, where you've got the flexor of the toes and
the flexor of the big toe, in the extensor compartment, the anterior compartment, you've
got the extensor of the big toe - extensor hallucis longus and the extensor of the digits
- so extensor digitorum longus.
So I've just removed the tibialis anterior, and we'll just have a look at this muscle
here, the extensor hallucis longus.
So if I just isolate that, so you can see it now here, it sits, it's not quite shown
here, but it actually sits medially on the fibula, on the middle half of the fibula and
it also attaches to the bit of the interosseus membrane that's adjacent to the fibula, so
it attaches here - its origin, and it descends along, anteriorly on the leg and crosses over
medially to insert here, at the base of the distal phalanx of the great toe.
So because of this muscle attachment, when this muscle contracts it extends the big toe
and because of its...because it's anchored here at the ankle, it can also dorsiflex the
ankle, so when it contracts it brings the toes up.
So if I just bring the other muscles back into view, you can see, well you can see these
two retinaculum, these are the extensor retinaculum, so you've got a superior and inferior retinaculum.
So these extensor retinaculum, they hold the extensor tendons in place, so I'll just remove
them for now, and you can look at the...well we'll look at the other side, we'll look at
the left side because I haven't removed the tibialis anterior.
So you can look at the relationship of these tendons, so the tibialis anterior tendon is
most medial, then you've got the extensor hallucis longus tendon in between the tendon
of the extensor digitorum longus, which I'll just talk about now, so it sits between the
extensor digitorum longus tendon and the tibialis anterior tendon on the anterior aspect of
the distal leg, so just worth noting that relationship.
So next we've got the extensor digitorum longus muscle, so the name gives away its function
- it extends, it's the long extensor of the digits.
So it attaches superiorly to the extensor longus muscle, so it's this muscle here, I'll
just isolate it.
So if we just take a look at the attachment, so we can see the extensor hallucis longus
muscle a bit inferiorly with its origin, and the extensor digitorum longus attaches higher
up on the proximal, medial surface of the proximal tibia, and it's also got this attachment
on the lateral condyle of the tibia - so that's its origin, and if we follow the muscle down
we can see that it splits to form four tendons which then attach to the digits.
So the insertion point of these, of the extensor digitorum longus is on the bases of the intermediate
and the distal phalanges.
So I'm not sure if it's actually shown on this model...no it's not, but the, this tendon
attaches to the bases of the middle and the distal phalanges.
So what this muscle does is it extends the lateral four digits, and it can also dorsiflex
at the ankle.
Okay, so the final muscle that I'm going to talk about is the, a small little muscle called
the fibularis tertius, or the peroneus tertius.
So I'll just remove away the other muscles, so we can take a look at this.
So I've just zoomed in a little bit and you can see this muscle here, this is the fibularis
tertius, or the peroneus tertius, and this muscle originates as you can see distally
on the medial surface of the fibula, so it's not that clear on this model here, but the
peroneus tertius, or fibularis tertius is often considered a part of the extensor digitorum
longus, and it's sometimes actually joined together with this muscle, so it runs down
into the foot and this tendon inserts medially on the base of the fifth metatarsals.
So what this muscle does is that it everts the foot and assists in dorsiflexing the foot.
So those are the muscles in the anterior compartment of the foot, sorry the leg.
So you've got the tibialis anterior, which you can see here.
You've got the extensor of the four toes, called the extensor digitorum longus, the
extensor of the big toe, the extensor hallucis longus and you've got the little peroneus
tertius, which is often thought of as part of the extensor digitorum longus.
So the way I remember the muscle of the anterior and posterior compartments is that the deep
layer of the muscles in the posterior compartment is quite similar to the muscles of the anterior
compartment.
So you've got the tibialis muscles.
So in the anterior compartment you've got the tibialis anterior, and in the posterior
compartment you've got the tibialis posterior.
And then you've got the muscles which act on the toes, the four toes, the four digits,
so you've got the extensor digitorum longus in the anterior compartment and in the posterior
compartment you've got the flexor digitorum longus.
And then you've got the muscle which acts on the big toe, so you've got the extensor
hallucis longus in the anterior compartment, and correspondingly you've got the flexor
hallucis in the posterior compartment.
And then you've got a little small muscle, so in the anterior compartment, the little
small muscle is the peroneus tertius, and in the posterior compartment the little small
muscle is the popliteus.
So that's just one way of thinking of these things, to help you remember different muscles
and how they act.