So now, we're going to move on to the medial compartment of the leg. The medial compartment
consists of six different muscles. We'll take a look at those now.
I'll just get rid of the sartorius and we can look at the medial compartment muscles.
These muscles originate in this area of the pelvis. The body of the pubis, the ischiopubic
ramus, this sort of area is where the muscles of the medial compartment originate. These
muscles are mainly innervated by the obturator nerve.
There's two muscles that are innervated by separate nerves. You've got the pectineus
muscle, which is this muscle here. That's innervated by the femoral nerve and you've
got the hamstring parts of the adductor longus muscle, which is innervated by the sciatic
nerve (the tibial branch of the sciatic nerve). Apart from that, they're all innervated by
the obturator nerve.
So these muscles, these group of muscles mainly adduct the femur at the hip joint. So I'll
the first muscle I'll talk about is this muscle, which is most medial and it runs vertically
down the medial aspect of the thigh. So this muscle is called the gracilis muscle. You
can see its course down the inside of the leg from the body of the pubis inserting onto
the medial surface of the proximal tibia. So it inserts just behind the insertion point
of the sartorius. This muscle adducts the thigh and it flexes the knee.
So next, we've got the pectineus muscle. You can see this muscle here. It's rectangular
in shape. It's innervated by the femoral nerve rather than the obturator nerve. I've just
isolated it here and you can see it originating here on the pectineal line and inserting onto
the femur. So what this muscle does, it adducts and flexes the thigh at the hip joint. That's
the pectineus muscle.
And then we've got a group of muscles called the adductor muscles. You've got the adductor
longus, the adductor brevis and the adductor magnus. This is the most superficial of the
adductor muscles and this is called the adductor longus. This muscle adducts and medially rotates
the thigh. The medial border of this muscle forms the medial border of the femoral triangle.
So I've just brought back the sartorius muscle just to explain the femoral triangle. The
femoral triangle is this area on the upper thigh. The superior border is the inguinal
ligament which runs from the anterior superior iliac spine down to the pubic tubercle. That's
the superior border.
Then you've got the lateral border formed by the medial border of the sartorius muscle,
this margin here. And then like I've just mentioned, you've got the medial border of
the adductor longus muscle, which forms the medial border of the femoral triangle. So
the femoral triangle is this region here.
So the adductor longus and the pectineus muscle adjacent to it form the medial part of the
floor of the femoral triangle. And then you've got the lateral part formed by the terminal
ends of the iliopsoas muscle. So that's just a quick bit about the femoral triangle.
We'll just take a look at the adductor longus muscle. You can see its origin on the femur
and the middle third of the femur.
I'm just going to dissect away some of these muscles. You've got the pectineus here. You've
got the adductor longus, which I've just shown you. I'm just going to remove that muscle,
so you can see what's beneath.
You've got this smaller muscle, which inserts on the femur a little higher up in the upper
third of the femur. This is called the adductor brevis. Remember 'brevis' means short in Latin,
so it's a shorter muscle. The adductor longus inserts further down here. So this muscle,
the adductor brevis muscle lies behind the pectineus and the adductor longus muscle.
This muscle adducts the thigh.
Most deep, we've got this huge muscle underneath. I'll just get rid of the adductor brevis and
we can see this big muscle here. This is called the adductor magnus muscle. 'Magnus' means
big or great in Latin, so it's the biggest adductor muscle and it's got two parts.
It's got a hamstring part, which is this part here, which runs up vertically. You've got
the adductor part, which is this part here. I've just isolated it to give you a good view.
So you've got the hamstring part, which runs vertically up and you've got the adductor
part, which is this part here.
So the hamstring part of the adductor magnus is innervated by the tibial branch of the
femoral nerve rather than the obturator nerve. So this part, the adductor part is actually
innervated by the obturator nerve and they've got two different origins.
So the hamstring part essentially descends vertically and it originates on the ischial
tuberosity, whereas the adductor part originates on the ischiopubic ramus. So this muscle adducts
and medially rotates the thigh.
So finally, we've got the obturator externus muscle. You can see this muscle here. It sits
on the lateral surface of the obturator membrane and it winds around behind the hip joint to
insert into an oval depression in the trochanteric fossa.
I just isolated it again here. You can see it sitting on the obturator membrane over
the obturator foramen and it winds around behind the hip joint and it inserts into this
little depression here, the trochanteric fossa. This muscle externally rotates the thigh.
So if you remember the obturator internus muscle, it sits on the medial surface of the
obturator membrane. So you can see that there and its 90° bend around. You can see the
obturator externus and internus.
So again, the obturator externus is innervated by the obturator nerve. So just bringing back
the muscles of the medial compartment, you've got two muscles, which aren't innervated by
the obturator nerve in the medial compartment. You've got the pectineus muscle, which is
this rectangular muscle here innervated by the femoral nerve and you've got the hamstring
part of the adductor longus muscle, which is innervated by the tibial branch of the
sciatic nerve. But apart from that, the rest are innervated by the obturator nerve.
Okay! So the final compartment of the thigh is the posterior compartment. The posterior
compartment is very simple because then you've got three muscles there. I'll just remove
the gluteus maximum to get a good look at this compartment.
The muscles in this compartment are innervated by branches of the sciatic nerve. These muscles,
apart from the short head of the biceps femoris muscle, these originate, all originate on
the ischial tuberosity. They run down to insert on the tibia. They extend the hip joint and
flex at the knee joint.
So you've got three muscles. You've got this muscle here, which sits laterally. This is
the biceps femoris muscle. It has two heads. You've got a long head, which originates on
the ischial tuberosity and you've got a short head, which originates on the femur. It inserts
onto the head of the fibula.
And then medially, you've got the semimembranosus muscle and the semitendinosus muscle. So a
way of remembering it is semimembranosus has an m in it, so m for media. Semimembranosus
and semitendinosus both have a semi- in it, so they both go together. They're both medial.
Because semimembranosus is medial, so semitendinosus is medial. And then because semitendinosus
has a t in it, so semitendinosus sits on 'top'.
So biceps femoris laterally and then you've got semimembranosus and semitendinosus medially
with semitendinosus sitting on the top.
So I've just isolated these muscles and you can see the origin of these muscles on the
ischial tuberosity. And then you can see the short head of the biceps femoris muscle originating
on the femur. So the long head and the short head converge into this common tendon and
then inserts onto the head of the fibula.
So the biceps femoris muscle extends at the hip joint and flexes at the knee joint. The
semitendinosus is the one that sits on the top and it's medial to the biceps femoris
muscle and it runs down and inserts on the medial surface of the proximal tibia. So it
inserts just behind the gracilis muscle.
So if I just bring the other muscles back in, you can see the gracilis here running
down and it inserts just behind the sartorius muscle, but just in front of the point where
the semitendinosus muscle inserts.
So the semitendinosus muscle, again, it flexes the knee and it extends at the hip. So the
semimembranosus muscle has the same action, extending at the hip and flexing at the knee
joint. It works together with the semitendinosus muscle. Let's just have a look at the insertion
point. It actually inserts behind on the medial condyle of the femur and it also inserts posteriorly
on the medial condyle of the tibia. And also, some of the fibers from the tendon blend with
the fascia which covers the knee joint.
So all these muscles of the posterior compartment or the three muscles of the posterior compartment
are innervated by the sciatic nerve, so the main function of these muscles is to extend
at the hip and flex at the knee.
So that's the muscles of the gluteal region and of the thigh. It's probably quite long,
but if you want to learn a bit more in detail about the various muscle actions and the points
of origin and insertion, then take a look at my individual tutorials where I cover it
in a bit more detail. Sorry if this was a bit more rushed, but feel free to rewind,
re-watch, whatever and take a look at my other tutorials.