The bones

The rib cage

Humans generally have 24 ribs, arranged as 12 pairs, and men and women have the same number. Add the sternum at the front and this page accounts for 25 of the 206 bones in the standard adult skeleton.

The first seven rib pairs are called true ribs because each reaches the sternum through its own strip of costal cartilage. OpenStax groups ribs 8 through 12 as false ribs because they do not attach to the sternum directly. The final two pairs, ribs 11 and 12, are also called floating ribs because they have no attachment to the sternum at all. Some anatomy sources reserve “false ribs” for pairs 8 through 10 and list the floating ribs separately, so a different total there may reflect a different classification rather than a different chest.

The sternum is one adult bone with three named parts. The manubrium sits at the top, the body makes up the long middle, and the xiphoid process forms the small tip below. Ribs meet the spine behind you and approach this breastbone in front, making a cage that can protect the heart and lungs while still moving with every breath.

These 4 entries account for 25 of the 206.How the 206 is counted.

On this page: Try one · Questions · The plates · The specimens · Nearby

01 · Try one

Can you name this one?

This is how the lab asks. A bone you name today comes back a week later to be named again, and that is how it stays known.

Identify the specimen

Flat bone in the center of the chest where the ribs meet.

1

sternum

plural: sternums

“breastbone”

In the body1

DescriptionFlat bone in the center of the chest where the ribs meet.

Field noteIt has three parts: the manubrium, the body, and the little xiphoid process at the tip, which only fully hardens in adulthood.

02 · Questions

The questions people ask about these bones.

How many ribs do humans have?

Usually 24, arranged as 12 pairs. Anatomical variations do occur, including an extra cervical rib in a small number of people. OpenStax, The Thoracic Cage and StatPearls, Ribs

Do men and women have the same number of ribs?

Yes. The standard human count is 12 pairs, with no separate count by sex. The old idea that men have one fewer is not part of human anatomy. OpenStax, The Thoracic Cage

What are true, false, and floating ribs?

True ribs, pairs 1 through 7, attach directly to the sternum through their own costal cartilage. In OpenStax's classification, pairs 8 through 12 are false ribs because they lack that direct attachment, and pairs 11 and 12 are also floating ribs because they do not attach to the sternum at all. OpenStax, The Thoracic Cage

Is the sternum one bone?

In the adult skeleton, yes. It has three parts called the manubrium, body, and xiphoid process. The xiphoid begins as cartilage and gradually turns to bone from middle age. OpenStax, The Thoracic Cage

03 · The plates

Every specimen with a plate of its own.

An engraved plate of the sternum — sternum1

An engraved plate of the rib — rib24 (12 pairs)

04 · The specimens

What each one is called, and how it is counted.

sternum

plural: sternums

“breastbone”

In the body1

DescriptionFlat bone in the center of the chest where the ribs meet.

Field noteIt has three parts: the manubrium, the body, and the little xiphoid process at the tip, which only fully hardens in adulthood.

On record

The sternum has three parts, and its small xiphoid tip starts life as cartilage before ossifying later. OpenStax 7.4
Clinicians can find the second rib by feeling the sternal angle, then count the ribs below it. OpenStax 7.4

rib

plural: ribs

“ribs”

In the body24 (12 pairs)

DescriptionCurved bones forming the protective cage around the heart and lungs.

Field note12 pairs: seven "true" pairs attach directly to the sternum; the other five are "false" pairs, and the last two of those float free at the front.

On record

The 12 rib pairs are grouped as seven true pairs, three indirectly attached pairs, and two floating pairs. OpenStax 7.4
A rib does not continue as bone all the way to the breastbone; its front end becomes flexible costal cartilage. OpenStax 7.4
A groove along a typical rib shelters a nerve and blood vessels beneath its lower edge. OpenStax 7.4

true rib

plural: true ribs

In the body14 (7 pairs)

DescriptionOne of the first seven pairs, each linked to the breastbone by its own strip of costal cartilage.

Field noteThe first seven pairs each reach the sternum through their own costal cartilage. Together with the other ribs, they move as the chest changes size during breathing.

On record

Each of the first seven rib pairs has its own costal-cartilage connection to the sternum. OpenStax 7.4
Their flexible costal cartilage helps the chest wall spring back during passive exhalation. StatPearls

false rib

plural: false ribs

In the body10 (5 pairs)

DescriptionOne of the final five pairs, without its own direct cartilage connection to the breastbone.

Field noteThe five pairs take two routes: ribs 8–10 join the cartilage above them, while ribs 11–12 reach no sternum at all and are called floating ribs.

On record

Ribs 8–10 connect to the cartilage above them, forming a chain that eventually reaches rib 7. OpenStax 7.4
Ribs 11–12 are “floating”: their front ends terminate in abdominal-wall muscle instead of reaching the sternum. OpenStax 7.4

05 · Learn them

Reading them is not the same as knowing them.

In the lab these are Case 03, The Chest, on the Explorer track. Case 12, The Rib Cage in Classes come later, on the Scholar track.

It introduces bones a few at a time, asks where they are, and comes back days later to check they stayed.

Start with theseBegin with four bones. It’s free, and you don’t need an account.

Nearby: arm and shoulder · leg · spine and pelvis · hand · wrist · foot and ankle · skull · ear · all nine