Bones of the Thoracic Wall
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Main Anatomy Index | Joints of the ribs
Last updated 30 March 2006
Bones of the Thoracic Wall
- The osteocartilaginous thoracic
cage is formed by part of the vertebral column
(12 thoracic vertebrae and intervertebral discs); 12
pairs of ribs and costal cartilages, and the sternum. The ribs and the
costal cartilages form the largest part of the thoracic
Thoracic Vertebrae (p. 33)
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- The special features of these vertebrae are: (1) they
have facets on their bodies
for articulation with the heads of ribs; (2) there are facets on their transverse processes
for articulation with the tubercles of ribs, except for
the inferior two or three ribs, and (3) they have long
The Costal Facets (p. 33)
- Thoracic vertebrae are unique in that they have facets on
their bodies and transverse processes for articulation
with ribs (T11 and T12 are exceptions).
- Two demifacets are located laterally on bodies of T2 to
T9. The superior demifacet articulates with the head of
its own rib and the inferior demifacet articulates with
the head of the rib inferior to it.
- T1 has a single costal facet for the head of the firs rib
and a small demifacet for the cranial part of the second
- T10 has only one costal facet which is partly on its body
and partly on its pedicle.
- T11 and T12 have only a single costal facet on their
The Spinous Processes (p. 33)
- Spinous processes of T5 to T8 are nearly vertical and
overlap the vertebrae like roof shingles.
- This arrangement covers the small intervals between the
laminae of adjacent vertebrae, thereby preventing sharp
objects such as a knife from penetrating the vertebral
canal and injuring the spinal cord.
- The spinous processes of T1, T2, T11 and T12 are
horizontal, and those of T3, T4, T9 and T10 slope
- There are usually 12 of these elongated
flat bones on each side of the thorax. They
form the largest part of the osteocartilaginous thoracic
- The ribs curve anteriorly and inferiorly from the
- Each typical rib has a head, neck, tubercle, and shaft.
- The head of a rib is
wedge-shaped and presents two articular facets for
articulation with the numerically corresponding vertebra
and the vertebra superior to it.
- These facets are separated by the crest
of the head.
- The neck of a rib is the
stout, flattened part located between the head and the
- The neck lies anterior to the transverse process of the
- Its superior border, called the crest
of the neck, is sharp, whereas its inferior
border is rounded.
- The tubercle of a rib is
on the posterior surface at the junction of its neck and
shaft and is most prominent on the superior ribs.
- The tubercles of most ribs have a smooth convex fact,
which articulates with the corresponding transverse
process of the vertebra, and a rough non-articular part
for attachment of the lateral
- The tubercles of the 8th to 10th
ribs have flat facets for articulation with similar
facets on the transverse processes of the vertebrae.
- The shaft (body) of a rib
is thin, flat, and curved. Forming its largest part, the
shaft has external and internal surfaces, thick and
rounded superior borders, and thin, sharp inferior
- A short distance beyond the tubercle, the shaft ceases to
pass posteriorly and swings sharply anteriorly.
- The point of greatest curvature is the angle
of the rib. Here the rib is both curved and
- The thorax of a person lying on his/her back is supported
by the angle of the ribs and the spinous processes of the
- The costal groove
(sulcus) and flange formed by the inferior border of the
rib protect the intercostal nerve and vessels that
accompany the rib.
True Ribs (p.
- The first seven (and
sometimes the eighth) pairs of ribs are called true or vertebrosternal ribs because
they are connected to the sternum
by their costal cartilages.
- The 8th to 12th pairs of ribs are
false or vertebrochondral ribs.
- Each of the 8th to 10th ribs is
connected by its costal cartilage to the ribs superior to
- The 11th and 12th pairs of false
ribs are often called vertebral or floating
ribs because they are unattached anteriorly.
- They end in the muscles of the anterior abdominal wall.
Ribs (pp. 35, 38)
- The 1st, 2nd, and 10th
to 12th pairs of ribs are atypical.
The First Rib (pp
- This is the broadest and most
curved of all the ribs. It is also the
shortest of the true ribs.
- The first rib is clinically important because so many
structures cross or attach to it.
- It is flat and has a prominent scalene
tubercle on the internal border of its
superior surface for the attachment of the scalenus anterior muscle.
- The subclavian vein
crosses the first rib anterior to the scalene tubercle
and the subclavian artery.
- The inferior trunk of the brachial
plexus passes posterior to it.
- A distinct groove is formed by the subclavian vessels and
brachial plexus on the superior surface of the first rib.
- This rib articulates with the body of the first thoracic
vertebra. The prominent tubercle of the first rib
articulates with the transverse process of this vertebra.
- The first rib is difficult to palpate due to the
clavicle, but the first intercostal space can be felt
just inferior to the clavicle.
The Second Rib (p.
- This rib has a curvature similar to the first rib, but it
is thinner, much less curved, and is about twice as long
as the first rib.
- It can easily be distinguished from the first rib by the
presence of a broad, rough eminence, which is the tuberosity for the serratus anterior
Rib (p. 38)
- This rib usually articulates with T10 vertebrae only.
11th and 12th Ribs (p. 38)
- These ribs are short, especially the 12th
- They are capped with a small costal cartilage, have a
single facet on their heads, and have
no neck or tubercle.
- The 11th rib has an ill-defined angle and a
shallow costal groove.
- The 12th rib has neither of these features and
may be shorter than the first rib.
Costal Cartilages (p. 39)
- These hyaline cartilage bars
are more rounded than the ribs, and extend from the
anterior ends of the ribs.
- The first seven, extend from the anterior ends of the
- These seven pairs (and sometimes the eighth) are
connected with the sternum.
- The 8th and 10th pairs of costal
cartilages articulate with the inferior border of the
cartilage of the preceding rib, and the costal cartilages
of the 11th and 12th ribs are
pointed and end in the musculature of the anterior abdominal wall.
- The costal cartilages contribute significantly to the
elasticity and mobility of the ribs.
Costal Margins (p. 39)
- The medial ends of the seventh to tenth costal cartilages
join to form a cartilaginous costal margin on each side.
Together, these margins form the costal
- The angle formed where the right and left costal margins
converge at the inferior end of the body of the sternum
is called the infrasternal angle.
It is located at the xiphisternal
joint, where the body of the sternum
articulates with the xiphoid process.
of the Ribs
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- The sternum (breastbone) is an elongated
flat bone that resembles a short broadsword or
dagger. It forms the middle part of the anterior wall of
- The sternum (G. sternon, chest) consists
of three parts: manubrium, body
and xiphoid process.
- The manubrium (L. handle), is the superior part of the
sternum. It is located anterior to T3 and T4 vertebrae.
- It is wider and thicker than the other two parts of the
sternum. Its narrow inferior end gives it a somewhat
- Broad and thick superiorly, the manubrium slopes
- The superior surface of the manubrium is indented by the jugular notch (suprasternal
notch), which can be easily palpated.
- On each side of this notch there is an oval articular
facet, called the clavicular notch,
which articulates with the medial end of the clavicle.
- Just inferior to the clavicular notch, the costal
cartilage of the first rib is fused with the lateral
margin of the manubrium.
- This is a flexible but strong primary cartilaginous
- The inferior border of the manubrium is oval and rough
where it articulates with the body of the sternum at the manubriosternal joint.
- The manubrium and body lie in slightly different planes;
hence, their junction forms a projecting sternal angle (angle of
- The bony landmark is located opposite the second pair of
- The sternal angle is an important
guide to the accurate numbering of the ribs.
Body of the Sternum (p. 41)
- The body of the sternum is the longest of the three
parts. It is located anterior to T5 to T9 vertebrae.
- It is longer, thinner, and narrower that the manubrium,
but its width varies owing to the scalloping of its
lateral borders by the costal
- The body is broadest at the level of the fifth pair of
sternocostal joints and then gradually tapers inferiorly.
- The anterior surface of the body is slightly concave from
side to side.
- In young people four sternebrae
are obvious. They articulate with each other at primary
- The sternebrae begin to fuse from the inferior end
between puberty and 25 years of age.
- In adults, the sternum is marked by three transverse
ridges marking the lines of fusion of the sternebrae may
be visible in a sternum from a young adult, but they are
less distinct that the ridges on the anterior surface.
Xiphoid Process (p. 41)
- This is a thin sword-shaped process (G. xiphos,
sword) is the smallest and most variable
part of the sternum. Although it is often
pointed, the xiphoid process (xiphisternum) may be blunt,
bifid, curved, or deflected to one side or anteriorly.
- The xiphoid is cartilaginous at
birth and remains so until early childhood. It
may begin to ossify during the third year of life and
then it consists of a bony core surrounded by hyaline
cartilage. However, ossification usually does not begin
until much later.
- The xiphoid usually ossifies and unites with the body of
the sternum around 40 years of age, but it may not be
united even in very old people.
- The xiphoid process is an important
landmark in the median plane for the following
reasons: (1) its junction with the body of the sternum at
the xiphisternal joint indicates the inferior limit of
the thoracic cavity anteriorly and the site of the
infrasternal angle; and (2) it is a midline pointer to
the diaphragmatic surface of the liver, diaphragm, and
inferior border of the hear.
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