Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we’re going to be talking about the bones of the ventral trunk.
And before I do so, I would like to define what is the trunk, the trunk of the human body. Well, basically, in anatomy, this is the central part of the human body—so what includes the thorax or chest cavity and also the abdomen. And right now, on the screen, we’re looking at the bones or some of the bones that define the trunk.
Now, important to add here that the trunk does not include the upper and lower limbs, the neck, and also the head. So all these structures are not included in the trunk.
And on this tutorial, we’re going to be looking at the important bony structures that can be seen on the ventral aspect of the trunk. And we will be focusing here on this bone known as the sternum and the related structures.
Now, we’re going to start off with the structure that you see on the screen, highlighted in green. It’s found on the sternum. This is known as the manubrium.
And the manubrium of sternum is a quadrangular part of the sternum that sits above the sternal angle, which is this angle right about here. And the manubrium is articulating with other structures that I would like to highlight here.
The first one or the first ones are the first and second ribs. So the first ribs, as you can see here on the image, and the second image… the second ribs are here. And you notice that these structures are articulating with the manubrium through their cartilages.
And notice here that the second ribs are only... or they’re articulating but partially with the manubrium of the sternum. So they’re not entirely articulating with the manubrium, as you see here on the first ribs.
The other structures articulating with the manubrium are the clavicles, and you can clearly see here these two clavicles articulating with this structure of the manubrium, known as the clavicular notch. And the clavicular notch will serve as articulating point for the clavicles to, then, articulate with the manubrium.
The other structure on our list, the final one, is the body of the sternum that is going to articulate inferiorly with the manubrium.
We’re going to move on to the next structure that we find on the ventral trunk. This is a joint, the sternoclavicular joint. And the sternoclavicular joint is a two-chambered joint or two-chamber synovial joint formed by the articulation between the clavicles and also the manubrium, as we’ve seen before.
Now, as I zoom in a bit, you can clearly see the articulation happening again, and this is known as... this is where the sternoclavicular joint happens.
The other structure is one that I already briefly mentioned, where the clavicles are going to be articulating on the manubrium. This is the clavicular notch. And the clavicular notch is an indentation found on either side of the upper part of the manubrium of the sternum.
Now, the manubrium articulates with the clavicles at this notch forming, then, the other joint that we talked about, the sternoclavicular joint.
The next structure on our list is going to be also a notch that we find on the manubrium, this is known as the suprasternal notch, also known as the jugular notch, and is a depression that you find on the upper border of the manubrium of the sternum. It’s quite visible and you can feel it just in your neck between the clavicles. You find a dip there, and this is where you can find the suprasternal or palpate. As we speak right now, you can try. This is where you find your suprasternal notch.
Now, we’re going to move on to another structure—this structure seen here, highlighted in green—a structure that I briefly mentioned on a previous slide. This is known as the sternal angle. And this is where the manubrium of the sternum will meet with this other part of the sternum known as the body and the angle. It will form an angle that you can even palpate in your chest, known as the sternal angle. It’s also commonly known as the angle of Louis.
The joint formed between the body of the sternum and the manubrium is a cartilaginous joint as a result of a symphysis.
Now, the sternal angle has different clinical importances for various reasons, including two that I would like to highlight on this tutorial. The first one, this marks the point or the sternal angle is going to mark the point where the aortic arch will begin and also end. It will also be the point where the trachea will bifurcate or split into two.
We’re going to move a bit more inferiorly on the sternum and talk about one of the structures that we briefly mentioned. This is the sternum… the body of the sternum or the sternal body. And the body of the sternum is the longest part of the sternum located between the manubrium.
As you can see, the manubrium is found superiorly. And inferiorly, we’re going to find this tiny process here known as the xiphoid process, which you can clearly feel just in the… between your chests. You’re going to... in the middle of chest, if you go a bit further down and palpate, you can feel a bit of the xiphoid process. So this is… it marks the end of the sternum body or the body of the sternum.
Now, also important to highlight here is that the body of the sternum will serve as an attachment point for one of the major muscles. So the anterior portion of the sternal body is going to serve as an attachment point for the pectoralis major.
Also if we zoom in, we can see some of the articulations happening here on the body of the sternum. So you can see that, laterally, you’ll find these indentations, these notches here that will serve as the articulating points for, here, partially for the second ribs. And then you will find full articulations with the cartilages of the third, the fourth, the fifth, the sixth, and also the seventh ribs—all happening on the lateral side of the sternal body.
And as I've just been mentioning about the different articulations happening or the different joints happening, this is the sternocostal joint that you see now on the screen. And the sternocostal joint is a joint that is formed by the articulation between the sternum and the different costal cartilages.
We’re going to end this tutorial with one of the structures that I briefly mentioned about on previous slides. This is the xiphoid process, seen here highlighted in green.
The xiphoid process is a cartilaginous structure that you find on the lower end of the sternum, just below the body of the sternum. And you can feel it. If you touch or if you palpate the middle of your chest, just go a bit further down, and you can feel at the end of the body of the sternum, you find the xiphoid process.
And the xiphoid process ossifies in adulthood.
And at the junction between the xiphoid process, as you can see, and also the body of the sternum, there is here an indentation or a notch that is going to be used for the articulation of the seventh rib. So this is where the seventh rib articulates with the sternum, and you can clearly see here on this image as well.