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 be absent.
The costal portion, which is the more extensive muscular part,
is gonna attach to the costal cartillages and the ribs,
and specifically, we're looking at the attachment of the costal part
to the costal cartillages and ribs of 7 through 12.
And that it's the costal portion on the right that forms a 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 wanna remember here is portions of the lumbar part
are gonna 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 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 mediale 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 of 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 esophagus,
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, at first, here, to 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 esophagus
passing from the thoracic cavity into the abdominal cavity.
This opening within the diaphragm is referred to as the esophageal 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 a 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 or Morgagni.
These are also potential sites of weakness and if they become too weak,
you can have herniation of abdominal viscera through these smaller openings.
These, again, are the major ones.
There are other small openings that will help transmit structures
between the thoracic and abdominal cavities.