The Pectoral Girdle - Online Tutor, Practice Problems & Exam Prep

The pectoral girdle, also known as the shoulder girdle, connects the arms to the axial skeleton and consists of the clavicle (collarbone) and scapula (shoulder blade). The clavicle articulates with the sternum and scapula, while the scapula features the acromion process and glenoid cavity, forming a ball-and-socket joint with the humerus. This structure allows for extensive arm mobility, making the shoulder the most flexible joint in the body. Understanding these components is crucial for grasping human anatomy and the mechanics of movement.

Pectoral Girdle

We're now going to move from talking about the axial skeleton, you know, those bones down the center of your body, to the appendicular skeleton, the bones of your arms and your legs. And what links the two is going to be the girdles. So we're going to start by talking about the pectoral girdle, and a girdle is just something that surrounds something else or binds something else. So the pectoral girdle surrounds the pectoral, or the thoracic region, the region of your chest. So, the pectoral girdle, we're also just going to start by saying it's sometimes called the shoulder girdle because the bones of the pectoral girdle make up the structure of the shoulder, and its job is to attach the arms to the axial skeleton. Now, quickly, some people have a misconception that the shoulder girdle or the pectoral girdle is going to be part of the skeleton because it's on the core of the body here. But it's really important to remember that technically, this is going to be part of the appendicular skeleton. When we think of the girdles, when we think of the pectoral girdles, we want to think of them sort of as parts of the arms and the legs.

Alright. So the pectoral girdle is going to be made up of two bones, and we're going to go through those now. First up, we have the clavicle. The clavicle, it's very likely you've heard before. It's called the collarbone, or the collarbones. And you can see the collarbone. You can see the clavicle. You can feel it very easily. You just start at your sternum here, you can touch it, you can walk your fingers across. It sort of comes out and curves around like the shape of your chest, comes back, and then it kind of swoops over to the tip of your shoulder there. So that medial side that we were just feeling that articulates with the sternum, and then the lateral side out at the tip of your shoulder there is going to articulate with the scapula. And we can see that in this image here. So we have an image, it shows the thoracic cage here kind of grayed out, and then we see the clavicle in purple. We have the medial side articulating with the sternum there. We feel it sort of swoops around like the shape of the chest, and then out, and it articulates with the scapula here at the edges there.

Now I have a clavicle here, and the word 'clavicle' actually comes from the Latin meaning key. And I guess some people thought that it maybe looks like an old tiny key. When I look at it, I always think that it kind of looks like something I could use to butter my bread. You could sort of hold it like this, and it has this flat part that you could spread butter or jam on your toast with. Now I don't recommend using human bones to spread butter, but if you did, choose the clavicle. Now when I look at this, I see that one end is really blunt and one end is really flat. That blunt end comes up, and that's the end that meets the sternum. And then it curves around, and that flat end comes out and articulates with the scapula at the acromion process. We're going to talk all about that now.

So we're going to look over here. We have the scapula. The scapula, I'm sure you've heard before called the shoulder blades. And you can see the scapula really easily when you look at someone's back, especially when they move their arms, because the scapula is really superficial. It's sort of stuck on the back there, and it moves when you move your arms. So it's going to articulate with the clavicle, just as we said, right up here at the tip of the shoulder, and it's also going to articulate with the humerus, or that upper arm bone. That's how the arm attaches to the body.

So first off, let's look at this acromion process, and that's going to be where it articulates with the clavicle. So we have an image down here, and we have two views. We have the anterior view here on the left, and the posterior view looking at it from the back here on the right. And I also have a scapula here. So this anterior view, you can see the scapula is very flat. So this is the part that would sort of go up against your back there. And you can see that on the posterior view, though, it has this sort of spine that comes up and this process that sticks out, and you can see it on our image here. This is the spine that comes up in this process right here, and then you can see this process here labeled 2 a. That process is going to make up the tip of your shoulder, and so that's called the acromion process. And remember, when we learned the regions of the body, 'acromion' meant the top of the shoulder, and it came from that same root as the 'acropolis.' And the acropolis ix the top of the hill in Greece, and the acromion process, that's the very top of your shoulder right here. And so if you touch that, you can feel you can walk it back, and you can feel the spine of the scapula there. You can feel the scapula. You can also walk it across the front, and you'll start walking onto the clavicle, and you can walk across right there.

Now the other thing that we want to note on the clavicle for now ix the glenoid cavity. This is going to be the depression for the joint. It's going to be the place where the arm comes in and makes the shoulder socket. So it's a ball and socket joint. This ix the socket. You can see it here in, labeled 2 b right here. We're also facing that part there, and we can look at on this bone here. You can see as a socket, it's very shallow. It's almost shaped more like a golf tee than it is like a real socket. And when you take the humerus and take the ball of the humerus and put it in there, that means that this humerus can move around a ton because it doesn't actually fit deep, deep into the joint. It just sort of has this shallow place to move around on. That's one of the things that makes your shoulder the most mobile joint in your body. Now the other things that contribute to that is that this scapula, well, it doesn't articulate with very much at all. It has that shoulder joint, the socket here for the humerus to go into, and then it also articulates with the clavicle up here at the acromion process, but that's it. And so when you move your shoulders, you can feel your scapulas moving. When you move your shoulders forward, you feel them rounding around your back there. When you move your shoulders back, you can feel pinching in the back. If you raise your arm, you can feel it sort of moving out a little bit. All that movement really contributes to being able to move your arms a ton, and that's even the clavicle, as you move your arm around, if you touch it, you can feel that it's moving too because on both ends of the clavicle, there are mobile joints. Now that's going to be very different than your pelvic girdle, your hip bones, where it has a pretty mobile joint where the leg attaches, but those bones themselves really don't move. Again, the scapula moves a lot.

Alright. We're going to be looking at that more in the example to follow, and I'll see you there.

The Pectoral Girdle Example 1

Our example tells me that the shoulder joint is the most mobile joint in the body, and it wants me to describe how the structures of the pectoral girdle aid in making the shoulder so mobile. And what it wants me to talk about, the glenoid cavity, the scapula, and the clavicle. Now as a visual aid, it shows me the pectoral girdle right here. It also shows me the humerus and the thoracic cage as a reference.

Alright. So first off, let's talk about the glenoid cavity. Do you remember how the glenoid cavity contributes to shoulder mobility? Well, we said the glenoid cavity, that's the socket in the ball and socket joint. And when we look at the scapula, we see it's really shallow. I said it's more like a golf tee than like a real socket. And when you take the humerus there, that means that it has a ton of mobility. It doesn't sit way in that that socket itself doesn't bind the humerus. So the glenoid cavity, we're going to start off just by saying that it is a shallow socket, and it being shallow allows that humerus to move around a lot.

Next, though, we want to just talk about the scapula in general. What about the scapula in general aids that shoulder mobility? Well, we said the scapula moves around a lot. Right? It's only articulated to the axial skeleton directly through the clavicle, and the attachment point's way out here at the acromion process. So when you move your arms, your scapula moves. Right? You can pinch it back. You can bring it forward. And when you're doing that, you're changing the angle of the glenoid cavity, which adds more mobility to that shoulder joint. So I'm going to say the scapula itself, I'm just going to sort of say that it is a mobile bone. It moves around a lot, and as it moves, it changes the orientation of that shoulder so you can move your arm even more.

Finally, it wants us to talk about the clavicle. So what about the clavicle aids in this mobility? Well, remember the clavicle, as you move your shoulder around, if you have your arm on it, you can feel the clavicle moving. So the clavicle itself, we said it has 2 mobile joints. And it again is going to allow that shoulder to change its orientation, to change the way that the glenoid cavity faces, to allow you to move your arm a lot.

Now this is all going to be in contrast to the pelvic girdle, which we haven't talked about yet. But the pelvic girdle where your legs attach, it's got a really deep socket and those bones aren't mobile. They don't move around. That's why you can swing your arm all around and you can't do it nearly as much with your leg. So next time you're raising your arm up above your head in class, remember you can put it up that high because of the glenoid cavity, the scapula, and the clavicle.

The medial end of the clavicle articulates with what structure?

• A. Scapula.
• B. Humerus.
• C. Ribs.
• D. Sternum.

Which statement about the scapula is correct?

• A. The scapula articulates with the ribs and the clavicle.
• B. The acromion process is the most medial point of the scapula where it articulates with the clavicle.
• C. The scapula is the largest bone of the axial skeleton.
• D. The glenoid cavity of the scapula articulates with the humerus.

Here’s what students ask on this topic:

What bones make up the pectoral girdle?

The pectoral girdle, also known as the shoulder girdle, is composed of two main bones: the clavicle and the scapula. The clavicle, commonly referred to as the collarbone, connects medially to the sternum and laterally to the scapula. The scapula, or shoulder blade, is a flat, triangular bone that articulates with the clavicle at the acromion process and with the humerus at the glenoid cavity. These bones work together to attach the arms to the axial skeleton and allow for a wide range of shoulder and arm movements.

What is the function of the clavicle in the pectoral girdle?

The clavicle, or collarbone, serves several important functions in the pectoral girdle. It acts as a strut that holds the scapula in place, allowing for proper shoulder alignment and movement. The clavicle also protects neurovascular structures that pass from the neck to the arm. Additionally, it transmits mechanical force from the upper limb to the axial skeleton, helping to stabilize the shoulder during arm movements. Its articulation with the sternum and scapula enables a wide range of shoulder mobility.

How does the scapula contribute to shoulder mobility?

The scapula, or shoulder blade, plays a crucial role in shoulder mobility due to its unique structure and articulations. It features the acromion process, which connects to the clavicle, and the glenoid cavity, which forms a ball-and-socket joint with the humerus. This shallow socket allows for extensive movement of the arm. Additionally, the scapula itself is highly mobile, capable of moving in multiple directions (e.g., elevation, depression, protraction, retraction), which further enhances the range of motion of the shoulder joint.

What is the glenoid cavity and its significance in the pectoral girdle?

The glenoid cavity is a shallow depression on the scapula that forms the socket part of the ball-and-socket joint with the humerus. This joint is known as the glenohumeral joint. The glenoid cavity's shallow nature allows for a wide range of motion, making the shoulder the most flexible joint in the body. However, this also makes the shoulder more susceptible to dislocations. The glenoid cavity's design is crucial for the extensive mobility required for various arm movements.

Why is the shoulder joint considered the most mobile joint in the body?

The shoulder joint, or glenohumeral joint, is considered the most mobile joint in the body due to its ball-and-socket structure, where the humerus fits into the shallow glenoid cavity of the scapula. This design allows for a wide range of movements, including flexion, extension, abduction, adduction, and rotation. Additionally, the scapula's mobility and the clavicle's articulations further enhance the shoulder's range of motion. This extensive mobility is essential for various daily activities and complex movements.