Hello anatomy friends this is Dr. Alsup and in this supplementary dissection video we will be discussing some of the muscles particularly associated with the abdominal wall, certain structures associated with the inguinal canal, and anything in that surrounding area. The inguinal canal is a traditionally difficult area in dissection so we will take our time in this region to discuss some of those basics that you need to know. But let's start with the abdominal wall first, specifically the most superficial of the anterolateral abdominal wall muscles, which are the external obliques. The muscle fibers of the external obliques run in a similar direction as those of the external intercostal muscles between the ribs.
I always think of kind of putting your hands in your front pockets in terms of the directionality of the muscle fibers for the external oblique. And if you're looking at a superficial dissection you are looking at the external oblique. You would have to reflect the external oblique to see the deeper internal oblique and transversus abdominis.
And as we aren't asking you to identify those you should be in pretty good shape there in terms of being able to identify this muscle. I also really like this image as it shows how the tendons of the oblique muscles really form the rectus sheath which is this whole muscle. area right here on this particular individual the rectus sheath is quite robust and they're essentially continuous because it is the tendons or the flattened tendons called the aponeuroses of the oblique muscles and transversus abdominis that form the rectus sheath. The sheath is pretty hard to miss. It is the dominant white and kind of variably opaque structure in the anterior portion of the abdominal wall.
You can see see through it a little bit in terms of seeing some of the muscle fibers but for the most part it's fairly opaque. And running down the midline you have umbilicus here so you know that you're in the midline is going to be the linea alba which means white line and it's notably more opaque than the rest of the rectus sheath and it's the medial most attachment point of those three anterior lateral abdominal muscles on both sides. Now let's see what we can see when we reflect a portion of the rectus sheath which has been done here.
In fact in order to review the rectus abdominis muscle you have to reflect the anterior portion of the rectus sheath which is what's happened in this image on the left side. The anterior rectus sheath has been left in place on the right side so you can really only see the left rectus abdominis. You can see how long the rectus abdominis is it extends from the xiphoid process up here all the way down towards the pubic symphysis so very long muscle and you can see the tendinous intersections that are going to be interspersed throughout the muscle here on this particular individual there are three on this side which is the most typical pattern. Now I put this second image over here with the rectus abdominis reflected inferiorly in order to point out that there is a posterior portion of the rectus sheath which you can see right in this region.
Remember that the rectus sheath is going to envelop the rectus abdominis. But it's not complete it actually ends about three-fourths of the way down and what you're left with in this inferior most portion is just transversalis fascia which typically appears a little more transparent than the posterior rectus sheath and this line of demarcation is called the arcuate line. All right let's move to the inguinal canal region and as I mentioned at the beginning this is a traditionally complex region. And there are a lot of structures that we're not going to have you identify we're really only picking up on the structures that are on the easier side to identify the more prominent structures. Now the inguinal canal extends from the deep inguinal ring which as the name would suggest is deep and not visible from these more superficial dissections, and the superficial inguinal ring which has been opened on this dissection it would be right about here.
But it is visible on this dissection so right here kind of where you have that opening is going to be the superficial inguinal ring. This is the exit or medial aperture of the inguinal canal and is formed by the external oblique aponeurosis and you can typically see structures exiting the canal. And you can see that in both of these images. We will start with this one where you can see the round ligament of the uterus exiting the where the superficial ring would be located.
And the round ligament is sometimes difficult to identify as it presents as a tubular collection of adipose tissue which may be difficult to differentiate from some of the surrounding adipose tissue. But one thing that you can see a little bit of here is that there and I drew already kind of a line through it is going to be a nerve called the ilioinguinal nerve which will run superficial to the round ligament. Sometimes that helps with identification, sometimes not so much it's a rather small nerve, but when you when you do see a collection of fat or adipose tissue with a nerve running right on top of it you're likely looking at that round ligament.
The round ligament of the uterus connects the uterus to the labia magis, although in some individuals it does not extend all the way to the labia magis into adulthood, and it's a remnant of the gubernaculum. On this individual you can see their spermatic cord exiting the superficial inguinal ring with that ilioinguinal superficial to it. And you can see on this side the spermatic cord has been dissected to show you the different components of the cord and we will discuss both the round ligament of the uterus and the spermatic cord in more detail in the reproductive anatomy session.
Now one last thing I want to discuss here is the inguinal ligament and you can't see it well here as recall that the inguinal ligament is the floor of the inguinal canal and we can still see these more superficial structures of the inguinal canal. So it's occluding the view of the inguinal ligament but we can conceptualize where it would be located as it extends from the anterior superior iliac spine to about the level of the pubic tubercle around this region and that is going to give you an indication that that inguinal ligament is longer than the inguinal canal. as it doesn't actually begin the inguinal canal doesn't actually begin until the deep inguinal ring which is a little bit more right around this region.
So that inguinal ligament is going to be made up of external oblique apneurosis and so it's going to be very similar in terms of composition as what we see right around this region. Okay moving to the deep surface of the anterior abdominal wall here and you can see peritoneal cavity over here you can see some of the the omenta right here a little bit of viscera this all looks a bit a little bit overwhelming I get that but there's a lot going on but let's take these things one at a time. So here this individual is actually holding the anterior abdominal wall that's been reflected and I can see kind of right off the bat one of the most prominent things is I see the inferior epigastric vessels so you can see the two paired veins and then the artery right in between and much of the peritoneum has been removed here so this is less the lateral umbilical fold than just the vasculature. Now just lateral to this you can see right around this region a collection or what looks like a tubular collection of adipose tissue is entering into this region here all right and that's exactly what is happening this is that round ligament of the uterus entering into the deep inguinal ring and so that area where you have the invagination of the transversalis fascia is the deep inguinal ring the entrance or internal aperture of the inguinal canal Now the round ligament tends to be a bit more robust around the deep inguinal ring than at the superficial inguinal ring but there is noted variation there.
Now important to note here in this image the inferior epigastric vasculature is going to be medial to the deep inguinal ring and that relationship is something that comes up often particularly in discussions of inguinal hernias. And lastly here is the trusty diaphragm so this is going to be the left hemidiaphragm and this over here will be the right. Diaphragm and we discussed the diaphragm in the previous block but it's just as important here as a major subdivision between the thoracic and abdominal cavity.
You can see the liver right underneath here with that very close relationship and the stomach is just going to be deep to Oops I had these mixed up this should be the left and this should be the right. Always patient left and patient right. See that gets us sometimes even though we think about these things quite often.
So that makes sense because the liver should be on the right. So right underneath the right hemidiaphragm will be the liver and right underneath the left hemidiaphragm which you can't see very clearly because it's not poking out underneath here will be the stomach. Apologies for that but you can see kind of on the fly how we can get those things confused.
Now recall that the diaphragm has three openings that allow structures to traverse the region. Recall the esophagus is going to traverse the region. You will have also the vagal trunks will be closely related to to that. You'll have the inferior vena cava. that will ascend through this region to get to the right atrium and of course you'll have the aorta which is also going to traverse the diaphragm in order to get to the abdominal cavity region.
Okay that should wrap us up regarding the musculature in this session and the inguinal canal structures and contents. Please take your time to review and reach out if you have any questions. I hope you have a great rest of your day.