Now, aponeurosis are really important. They
are just like a tendon, like your biceps attaches
to your radius in your arm. They are very
thin and quite strong tendon. But, for these
anterolateral abdominal wall muscles, the
tendon is only flat and forms a kind of fibrous
sheath and these are known as aponeurosis.
And these aponeurosis form what?s called
the rectus sheath. And on the body plan, we
can remember that we have got the midline
running down here and then we have got our
semilunar lines. Remember, those semilunar
lines from the surface anatomy talk. Well,
these semilunar lines form the lateral boundary
of a structure known as the rectus sheath.
We can see them here where we have got the
midline and we can make out the indentations
of rectus abdominis and then we have the semilunar
lines here. And these form the boundaries
of what?s known as the rectus sheath.
This is formed by the aponeurosis from these muscles
coming around and interdigitating around rectus
abdominis to unite in the midline and we can
see this here. Now, this is a particularly
complicated image. So, I have to take some
time in explaining it, but what we can see
is a transverse section through the abdomen.
So, it?s like someone?s just chopped me
in half and you are looking down on to the
So, we can see, what we have is the posterior
aspect which is down here. So, this is your
back and then here, this is anteriorly here.
So, that?s where your umbilicus is.
This is in the midline here. So, this is where
your linea alba is going to be located.
And what we have radiating from the posterior
aspect of these anterolateral abdominal wall
muscles, we can see we have three of them
again. We have 1, 2, 3. We have our external
oblique, internal oblique and transversus abdominis.
We have got these three muscles. But, what
you notice is the actual muscle tissue which
is here in orange, doesn?t run all
the way to the midline. The musculature
stops just before it gets to the rectus abdominis
muscle here. So, this is where we find our
semilunar lines, just here, the lateral extension
or the lateral boundary of the rectus sheath,
of rectus abdominis muscle here. And what
we find is that these aponeurosis from muscles
external oblique, internal oblique and transversus
abdominis interdigitate around rectus abdominis
as they pass towards the linea alba in the
midline. The formation of the rectus sheath
differs and this is where above and below
comes in. It differs, if you are above
or below the umbilicus. Now, this is the level
of the umbilicus, this here. This is the umbilicus
just here. So, if you are above the umbilicus
or if you are below the umbilicus, this arrangement
is going to be different.
So, let's have a look. If we are above the
umbilicus, we are looking at the details now
of the rectus sheath above the umbilicus and
that?s this one here. So, imagine that this
line here is coming... just like this one,
coming from the posterior aspect. So, it?s
taken higher up above the umbilicus. We are
looking at the formation of the rectus sheath.
We can see that here we have external oblique,
here we have internal oblique and here we
have transversus abdominis. We can see the
anterior... this is the rectus sheath anteriorly,
we have the aponeurosis of external oblique
and posteriorly, behind rectus abdominis,
we have the aponeurosis of transversus abdominis.
So, anteriorly to the rectus abdominis muscle,
we have the aponeurosis of external oblique
and posterior to rectus abdominis, we have
the aponeurosis of transversus abdominis. So,
what happens to internal oblique?
Well, the internal oblique muscle, as it approaches
rectus abdominis, splits into two.
So, the aponeurosis of internal oblique splits into
two lamina, an anterior lamina and a posterior
lamina. So, we have the anterior layer of
internal oblique aponeurosis.
Posteriorly, behind rectus abdominis, internal oblique
sends a layer that goes behind rectus abdominis.
So, posterior, we have the posterior layer
of internal oblique aponeurosis.
So, if we were to go from anterior to posterior, we
would find the aponeurosis of external oblique.
We?d then find the anterior lamina or the
anterior layer of internal oblique,
we?d then find rectus abdominis. Carrying on posterior,
we?d then have the posterior lamina or layer
of internal oblique and then we would have
the aponeurosis of transversus abdominis.
So, effectively would have one and a half
anteriorly and one and a half posteriorly
where the two halves have come from internal
oblique dividing. And then most posterior,
we then have a fine layer which is called
transversalis fascia and then we have the
peritoneum. We will explore those in later
classes, in later lectures. So, that?s above the umbilicus.
If we now go below the umbilicus... If we
now go below the umbilicus, then this is a
lot simpler. So, previously, we had the section
above and now, we have made a section below
the umbilicus. So, now, we are concentrating
on this one. Similar orientation of muscles.
Here, we have got rectus abdominis radiating
around here. We are mentioning that this is
attaching to the posterior wall again, so
a similar arrangement, but this time,
the aponeurosis from all three anterolateral abdominal
wall muscles, all three, external oblique,
internal oblique, transversus abdominis, runs
anteriorly. Internal oblique doesn?t split
and transversus abdominis aponeurosis passes
anterior to rectus abdominis.
So, the only thing we have posterior to rectus abdominis
is that membrane I spoke about, transversalis
fascia, and then the peritoneum. We can see
it here. External oblique, internal oblique,
transversus abdominis. We can see that the
aponeurosis from these muscles all pass anterior
to rectus abdominis. So, we can see that above
and below the umbilicus, the rectus sheath
is very different. Above it, internal oblique
is divided, lamina goes anterior and lamina
goes posterior and below the umbilicus, all
three aponeurosis pass anterior to rectus
abdominis to then merge with the linea alba.
So, that?s the rectus sheath. It?s a very,
very important arrangement.