Which bones form the chest: the sternum, 12 pairs of ribs and the thoracic vertebrae

What the chest bones are called

Together they form the thoracic cage, which most people call the rib cage. The OpenStax chapter on the thoracic cage, hosted by LibreTexts, defines it as the 12 pairs of ribs with their costal cartilages and the sternum, anchored behind to the 12 thoracic vertebrae, T1 to T12. The chapter gives its role as protecting the heart and lungs.

Four names cover everything you will be asked to point at:

• Sternum: the breastbone, a flat bone down the front of the chest.
• Ribs: curved, flattened bones numbered 1 to 12 from the top, matching the thoracic vertebra each one meets.
• Costal cartilages: bars of hyaline cartilage that carry most ribs forward to the sternum. They are not bone, but they are part of the cage.
• Thoracic vertebrae: the middle segment of the spine, the only vertebrae that carry ribs.

The clavicle and scapula sit on the upper chest, yet neither belongs to the thoracic cage. They make up the shoulder girdle, covered in our guide to the bones of the shoulder. The clavicle meets the sternum at the sternoclavicular joint, on the upper corner of the manubrium.

Which bones make up the chest wall

This table lists every piece of the chest wall with its count and position, plus what it joins. It answers the basic question on its own:

The thorax chapter of O'Rahilly's Basic Human Anatomy, published by Dartmouth, uses a slightly wider frame. Its skeleton of the thorax takes in the sternum, the ribs and their cartilages, the thoracic vertebrae and the intervertebral discs between them. The discs are not bone either, so they never change a bone count.

How many bones are in the rib cage: 25 or 37

The answer depends on whether the vertebrae count. In the standard tally of 206 bones, the thoracic cage gets 25: 24 ribs plus the sternum. The 12 thoracic vertebrae are counted with the vertebral column instead, so they are not added twice.

If a question asks for every bone that encloses the chest, the 12 vertebrae join the count and the total becomes 37. Read the wording before you answer:

• "Thoracic cage" or "rib cage" in a 206 count: 25.
• "Skeleton of the thorax," including the spine behind: 37.

The sternum counts as one bone even though it has three named parts. Its lowest part, the xiphoid process, starts out as cartilage. LibreTexts says it ossifies gradually from middle age, and O'Rahilly describes it as a small, variable piece of hyaline cartilage with a bony core.

The number of ribs is the one fixed point. Our atlas notes that men and women have the same number, and that about 1 person in 200 has an extra, 13th pair. O'Rahilly adds that such a supernumerary rib can appear in the neck or the lumbar region.

The sternum and its three parts

From top to bottom come the manubrium, the body and finally the xiphoid process. Each part receives particular ribs, which is why the sternum is the best place to start counting:

• Manubrium: the wide upper part. Its top border is the jugular, or suprasternal, notch, and on each side a clavicular notch takes the end of the clavicle. The first costal cartilage attaches to its side.
• Body: the long central part, about twice as long as the manubrium according to O'Rahilly. It has notches on each side for costal cartilages 2 to 7.
• Xiphoid process: the small lower tip, which receives no rib.

The manubrium and body meet at the sternal angle, a slight bend that you can feel as a transverse ridge. O'Rahilly places it about 5 cm below the jugular notch, at the level of the T4 or T5 vertebra. The second costal cartilage attaches there, so the angle tells you where rib 2 is.

The sternum page in our Bone Atlas adds the joints at each end: a saddle joint with the clavicle and a cartilaginous joint between manubrium and body.

True, false and floating ribs, by number

The ribs fall into groups according to how their costal cartilage reaches the sternum. This table gives the version used by both of our sources:

So every floating rib is also a false rib. LibreTexts and O'Rahilly both put ribs 8 to 12 among the false ribs, with 11 and 12 as the floating pair. Some summaries, including our own atlas entry, call only 8 to 10 false and list 11 and 12 separately. If your course uses that split, the numbers on the table stay the same and only the label changes.

O'Rahilly adds that the ribs and their cartilages grow longer from the first to the seventh, and that their downward slope increases from the first to the ninth.

Where each rib meets the spine

A typical rib has a head and a neck, then a long shaft. The head articulates mainly with the body of its own vertebra and, to a lesser degree, with the vertebra above. A small bump called the tubercle articulates with the transverse process of its own vertebra. Just beyond the tubercle comes the angle, where the rib curves most. LibreTexts notes that in the anatomical position the rib angles line up with the medial border of the scapula.

O'Rahilly calls ribs 3 to 9 the typical ribs and singles out the others:

• Rib 1: short, with a flat upper surface. Its head meets T1 only.
• Rib 2: much longer than the first and meets the bodies of T1 and T2.
• Rib 10: usually meets T10 only.
• Rib 11: meets T11 only, and its tubercle, angle and costal groove are all indistinct.
• Rib 12: a small, slender rib of variable length that meets T12.

Along the lower inner edge of each typical rib runs the costal groove, which shelters the intercostal vein, artery and nerve, in that order from above. The ribs page in our atlas covers each feature with its joints.

How to find and count the bones of your own chest

You can check most of this on yourself. Start at the jugular notch, the dip at the base of your neck between the inner ends of the clavicles. Slide a finger down about 5 cm until you meet the transverse ridge of the sternal angle, then move sideways onto the second costal cartilage and the second rib.

Count down from there. O'Rahilly explains why you do not start higher: the first rib is hidden behind the clavicle and hard to feel, so counting begins at rib 2. The gap you feel just below the clavicle is the first intercostal space.

Lower down, the xiphoid process lies in the epigastric fossa, which O'Rahilly also calls the pit of the stomach. On a mounted skeleton, finish by counting 12 ribs on each side and checking which ones reach the sternum on their own cartilage. When you review from photos, Osteo+ names a bone from a picture, so you can check a loose rib or sternum before moving on.

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