The sternalis part specifically is shown here
when we start to look at these parts individually.
It’s bilateral and so, you have a little
bit of intervening space here. It’s attaching
to the xiphoid process, one of the three bony
elements that constitute the sternum. The
sternalis portion in some individuals may
The costal portion, which is the more extensive
muscular part, is going to attach to the costal
cartilages and the ribs. And specifically,
we’re looking at the attachment of the costal
part to the costal cartilages in ribs of 7
through 12. And it’s the costal portion
on the right that forms the right dome and
it’s the costal portion here on the left
that will contribute to the formation of the
left dome of the diaphragm. So, please keep
that in mind.
The lumbar portion has multiple attachment
points. And what you will want to remember
here is portions of the lumbar part are going
to attach to lumbar vertebrae. And then we
have some other portions of the lumbar part
that will attach lateral to the lumbar vertebrae.
And so, if we take a look at what we have
going on, we have a couple of ligaments that
we see here and here. We see the same ligaments
on the left side of the body here and here.
This is the medial arcuate ligament. Here
it is on the right side. And then we also
have one that lies lateral and that is the
lateral arcuate ligament on the right side
of the body. And then we have the left arcuate
ligament. So, the lumbar portions have attachments
to those two ligaments.
In addition, we have this portion here, the
lumbar part. This is called the right crus
and it’s attaching to lumbar vertebrae L1
down to L3, L4. And a portion of the right
crus will wrap around the oesophagus, as we
see here, and come back to the right side.
The left crus is this area of the lumbar part
right along here. The left crus will attach
to lumbar vertebrae L1, L2 and perhaps even
as well as L3.
There are openings or apertures within the
diaphragm. Our focus here is on, first here,
the three largest openings and these will
transmit structures so that you can have structures
travelling from the abdominal cavity
into the thoracic cavity or vice versa.
The first opening here to take a look at is
this area here. This is the caval opening.
This is what transmits the inferior vena cava.
And you can see the wall of the inferior vena
cava in blue with the lumen. Once the inferior
vena cava passes through this aperture, the
right atrium lies just immediately above and
the inferior vena cava will empty into the
right atrium. The vertebral level here is
T8. Sometimes it’s described as being between
T8 and T9, but we’ll just keep it simple
here and say it’s at T8.
We also have, in this location, we have an
opening for the oesophagus passing from the
thoracic cavity into the abdominal cavity.
This opening within the diaphragm is referred
to as the oesophageal hiatus. The vertebral
relationship of this hiatus is at vertebral
level T10. In some situations, there can be
a hiatal hernia. So, there’s a weakening
within this hiatus and as a result, the stomach
can herniate through the hiatus and portion
of it will then occupy the thoracic cavity.
The last aperture passes behind the diaphragm
between the right crus and the left crus.
This is your aortic hiatus and it allows the
passage of the thoracic descending aorta into
the abdominal cavity. So, it becomes the abdominal
aorta. And this is at vertebral level T12.
We can also see here a smaller opening on
either side of the sternal parts of the diaphragm.
And so, right along here between the sternal
part and the costal part, you have a triangular
area called the sternocostal triangle and
you have one on the opposite side as well.
These are also known as the foramina of Morgagni.
These are also potential sites of weakness
and if they become too weak, you can have
herniation of abdominal viscera through the
smaller openings. These again are the major
ones. There are other small openings that
will help transmit structures between the
thoracic and abdominal cavities.