Description

Ribs and Sternum Anatomy | Bones of the Thorax

Structures covered in this video:

Rib Classification by Sternum Connection:
• True ribs (Ribs 1–7)
• False ribs (Ribs 8–10)
• Floating ribs (Ribs 11–12)

Rib Classification by Structure:
• Typical ribs (Ribs 3–9)
• Atypical ribs (Ribs 1, 2, 10, 11, 12)

External and Internal Anatomy of a Typical Rib (e.g., Rib 4):
• Costal end / Sternal end (Extremitas costalis)
• Head of rib (Caput costae)
• Superior articular facet (Facies articularis superior)
• Inferior articular facet (Facies articularis inferior)
• Crest of the head (Crista capitis costae)
• Neck of rib (Collum costae)
• Tubercle of rib (Tuberculum costae)
• Articular facet of tubercle (Facies articularis tuberculi costae)
• Angle of rib (Angulus costae)
• Body/Shaft of rib (Corpus costae)
• Costal groove (Sulcus costae)

Atypical Rib Features:
• First rib
• Scalene tubercle (Tuberculum musculi scaleni)
• Groove for subclavian vein (Sulcus venae subclaviae)
• Groove for subclavian artery (Sulcus arteriae subclaviae)
• Second rib
• Tuberosity for serratus anterior (Tuberositas musculi serrati anterioris)
• Tenth to twelfth ribs
• Single articular facet
• Absence of neck and tubercle (Ribs 11 & 12)
• Free anterior ends

Muscle Attachments and Clinical Notes:
• Scalenus anterior and medius insertion on first rib
• Serratus anterior origin on first and second ribs
• Latissimus dorsi and quadratus lumborum on floating ribs
• Thoracic outlet syndrome and subclavian vessel relationships
• Common rib fracture site at rib angle
• Intercostal neurovascular bundle in costal groove

Sternum Anatomy:
• Manubrium (Manubrium sterni)
• Jugular notch (Incisura jugularis)
• Clavicular notches (Incisurae claviculares)
• First costal notch (Incisura costalis prima)
• Body of sternum (Corpus sterni)
• Costal notches for ribs 2–7 (Incisurae costales)
• Xiphoid process (Processus xiphoideus)
• Diaphragm, rectus abdominis, and transversus thoracis attachment
• Sternal angle (Angulus sterni)

Thoracic Apertures:
• Superior thoracic aperture
• Inferior thoracic aperture

Connections to Surrounding Structures:
• Costal cartilages
• Clavicle articulation (Sternoclavicular joint)
• Rib articulation (Sternocostal joints)
• Thoracic cage structure and function

Clinical anatomy and relevance:
• CPR-related xiphoid fractures
• Central venous access landmarks
• Rib fractures and costal groove neurovascular damage
• Palpation of sternal angle and rib counting

Sources:
• Kozlowski, T. (2017). Memorix Anatomy, 2nd ed.
• Standring, S. (2020). Gray’s Anatomy, 42nd ed.
• Tubbs RS, Shoja MM, Loukas M. (2016). Bergman’s Encyclopedia of Human Anatomic Variation
• White TD, Folkens PA. (2005). The Human Bone Manual

Programs used: Complete Anatomy, Biorender, PowerPoint

Transcript

Introduction & Content
0:00
Now we’re covering the bones of the thorax. These include all twelve
0:03
pairs of ribs, and the sternum in the center. So here’s what we’re going to talk about. First,
0:08
we’ll go through the structures of the ribs, what makes them true and false,
0:12
or even typical and atypical ribs. Then we’ll cover the sternum, its
0:16
different parts and how it connects to the ribs. And at the end, we’ll put it all together with
0:21
a quick look at the rib cage as a whole. What’s up everyone, my name is Taim. I’m
0:25
a medical doctor, and I make animated medical lectures to make different topics in medicine
0:29
visually easier to understand. If you’d like a PDF version or a quiz of this presentation, you can
0:34
find it on my website, along with organized video lectures to help with your studies.
0:37
Alright, let’s get started. The ribs are long, curved bones
Ribs Anatomy
0:41
that form a protective cage around the heart and lungs. We have twelve pairs in total,
0:47
numbered from top to bottom. It’s easier to count them if you count from the back,
0:50
where they attach to the vertebrae. Interestingly, each rib connects to the spine at the back,
0:55
but not all of them connect to the sternum the same way. That’s why we can classify
1:00
them based on how they articulate with the sternum, and because some of these ribs have
1:05
the same structure, and some a little bit different, we can also classify them based
1:09
on structure. So two ways to classify ribs. Now, let’s go ahead and complete the ribcage
True vs False Ribs
1:15
by adding the costal cartilage, which is cartilage connecting the ribs to the sternum,
1:20
First, we have the true ribs, these are ribs one through seven. They’re called true because
1:26
they each connect directly to the sternum through their own individual costal cartilage.
1:32
Next are the false ribs, ribs eight, nine, and ten. These don’t have a direct connection to the
1:37
sternum. They instead share a common cartilage that merges with the cartilage of the rib above,
1:43
forming an indirect link. Makes sense? What about the last two?
1:48
The last two ribs, ribs eleven and twelve are the floating ribs. They don’t connect to the sternum
1:54
at all. They end freely in the posterior abdominal wall, which gives them their name. Floating ribs.
2:00
So, this is one way to classify these ribs. True, false, and floating ribs, all based
2:06
on how they articulate with the sternum. But we can also classify ribs based on their structure.
Typical Rib
2:12
Now let’s look at the ribcage as a whole, and for this next part,
2:16
we’ll take rib number four as an example. We’ll isolate it, and then zoom in, and go through
2:22
its external and internal anatomy step by step. At the very tip of the rib, we have the costal
2:28
end, also called the sternal end or extremitas costalis. This is the flattened, anterior tip of
2:34
the rib, where the costal cartilage would normally attach, and helps bridge the rib to the sternum.
2:39
Posteriorly, we have the neck of the rib. This is the short, narrow portion of bone that lies just
2:45
behind the head of the rib. The head of the rib is rounded and attached to the vertebra, how does
2:50
it look like? Let’s rotate the rib a little bit. Here we can see two articular facets. These facets
2:57
connect to the vertebral bodies, one articulates with the numerically corresponding vertebra,
3:02
and the other with the vertebra above as you see here. Between these two facets,
3:07
there’s a small ridge called the crest, which serves as an attachment site for the
3:11
intra-articular ligament of the costovertebral joint. Joints will be covered in the next video.
3:16
Next to the head, on the posterior surface, we can see the tubercle. This part has two regions:
3:22
a rough non-articular portion and a smooth oval facet, called the articular facet of the tubercle,
3:29
which connects with the transverse process of the corresponding thoracic vertebra as you see here.
3:34
Then the rib begins to bend. This point of maximum curvature is called the angle of the rib. It’s
3:40
clinically important because this is where the rib is weakest and most likely to fracture.
3:46
Following that, we get to the long portion called the body or shaft. It’s thin, flat, and curved,
3:52
forming most of the rib’s length. The rib has an internal surface facing the thoracic cavity,
3:58
and an external surface, facing outward, serving as an attachment site for thoracic muscles. On
4:04
the internal surface of the body, near the inferior border, we see a shallow groove,
4:09
called costal groove. This groove contains the intercostal vein, artery, and nerve.
4:16
So, this is the general structure of what we call a typical rib. Most ribs, especially ribs 3 to 9,
4:22
have all the structures we just went through, so we call them, typical ribs. Atypical ribs like the
Atypical Ribs
4:29
first and second. Also the tenth, eleventh, and twelfth have some slight variations. For example.
4:35
Here you see the first and second ribs. These are both considered atypical ribs because they
4:41
don’t follow the same pattern as the typical ribs we just covered. The first rib is the shortest
4:46
and broadest of all twelve, and it lies almost horizontally in the upper thorax. It has the
4:52
most pronounced curve of any rib and plays a role in defining the anatomy of the root of the neck.
4:58
Alright what do we see? The first thing to notice are the muscles that attach to it. We
5:02
see the scalenus anterior muscle, which inserts onto a small bony bump on the superior surface.
5:08
Just behind this is the scalenus medius muscle, which attaches to the posterior portion of the
5:14
rib’s upper surface. These two muscles create a space between them, and that’s where we find the
5:20
subclavian artery. The subclavian vein lies anteriorly. This relationship is clinically
5:26
important, especially when performing central venous access or evaluating thoracic outlet
5:31
syndrome. Also visible here is the serratus anterior muscle, which originates on the outer
5:37
surface of the rib, just lateral to these grooves. So, what structures can we take out of this? We
5:43
can see the scalene tubercle in the center. The groove posterior to the tubercle accommodates
5:48
the subclavian artery, while the groove anterior to it accommodates the subclavian vein. On the
5:54
second rib, we can see the roughened area where the serratus anterior muscle attaches to, known
6:00
as the tuberosity for serratus anterior. These are important surface landmarks when identifying
6:06
the first rib in dissection or imaging. Now let’s zoom out and look at the rib cage as a
6:12
whole again. We’ve covered the first and second ribs, and next we’ll go down to the remaining
6:17
atypical ribs: the tenth, eleventh, and twelfth. What makes these three ribs atypical is that they
6:24
only have one articular facet on their head. That means they articulate with a single vertebral
6:30
body, unlike the typical ribs which articulate with two. The tenth rib usually has this single
6:35
facet and otherwise resembles the typical rib, but the eleventh and twelfth ribs are more distinct.
6:41
They don’t have a neck or a tubercle, and they end freely in the posterior abdominal wall without
6:47
attaching to the sternum, remember? Floating ribs we call them. They have a pointed anterior end and
6:53
serve as attachment points for muscles like the latissimus dorsi and quadratus lumborum.
6:59
So, we got typical and atypical ribs, and this is how we generally divide the ribs in our body.
Sternum
7:05
Anatomically at least. Next, let’s do the sternum. We will isolate it, and then zoom in.
7:11
The sternum. This flat, elongated bone consists of three main parts. First we have the manubrium,
7:18
the broadest and thickest part of the sternum. It serves as a point of articulation for the
7:24
clavicles and the first pair of ribs. Its superior surface is concave and slopes slightly downward as
7:31
it meets the next part, the body of the sternum. And inferior to the body, we find the xiphoid
7:36
process, the smallest and most variable part of the sternum. It’s often cartilaginous in younger
7:42
individuals, and ossifies with age, and it also serves as an attachment site for the diaphragm,
7:48
rectus abdominis, and transversus thoracis. Interesting thing with the xiphoid is that,
7:52
if you ever need to do CPR on someone, if you place your hand too low on the sternum, you can
7:58
actually fracture this part, risking injury to underlying organs like the liver. But, you know,
8:03
you’d rather break a bone and save the life. Now, between the body and manubrium, we can
8:09
see the sternal angle. At the superior border of the manubrium we can see the jugular notch,
8:15
which is a depression that can often be palpated at the base of the neck. Just lateral to the
8:20
jugular notch are the clavicular notches, which articulate with the medial ends of the clavicles,
8:25
forming the sternoclavicular joints. These are the only true synovial joints
8:29
connecting the axial skeleton to the upper limb. On each side of the manubrium, just inferior to
8:35
the clavicular notches, we see the first costal notches, which receive the costal cartilages of
8:41
the first ribs. These are unique because the first ribs articulate only with the manubrium,
8:46
not with the body of the sternum. Inferior to this, along the lateral margins of the body,
8:51
we find the remaining costal notches, which are articulation points for the
8:56
costal cartilages of ribs 2 through 7. The second costal cartilage articulates at the sternal angle,
9:02
giving us a clear landmark for counting ribs in clinical exams.
9:06
Now let’s add the surrounding bones of the thorax. Here you can see the clavicles articulating at the
9:12
clavicular notches, the ribs attaching via their costal cartilages into the series of
9:17
costal notches, and the xiphoid process projecting downward at the inferior end. This orientation
9:23
gives the sternum its structural role as the central anterior support for the thoracic wall.
9:29
So that was the detailed anatomy of the ribs and the sternum. Now, when you look at the thorax as
Thorax
9:35
a whole. At the top, we have the superior thoracic aperture, bordered by the manubrium, first ribs,
9:41
and the T1 vertebra. This is a narrow opening through which the trachea, esophagus, subclavian
9:47
vessels, and brachial plexus pass between the thoracic cavity and the neck. Inferiorly, we have
9:52
the inferior thoracic aperture, a wide opening formed by the xiphoid process, costal margins,
9:58
and the twelfth thoracic vertebra. This opening is closed off by the diaphragm, separating the
10:03
thoracic cavity from the abdominal cavity. But of course, the thoracic skeleton isn’t
10:08
just bones. It’s held together by joints, like the sternocostal and costovertebral joints,
Outro
10:14
and by connective tissues that create a sealed and dynamic thoracic cavity. These joints
10:19
and membranes allow for respiration while also protecting the organs inside. In the next video,
10:25
I’m gonna take you through the joints of the thoracic bones and how the ribs articulate. So
10:30
click on the next video, and I’ll see you there. If you want a handmade PDF version of this
10:34
lecture, take a quiz to test your knowledge, or access an organized list of all my videos,
10:38
you can find everything on my website. Thanks for watching! See you in the next one.