The thoracic wall consists of bones including the sternum, ribs, and thoracic vertebrae. The sternum has three parts - manubrium, body, and xiphoid process. There are 12 pairs of ribs which can be typical or atypical. Costal cartilages connect the ribs to the sternum. Between the ribs are intercostal spaces containing muscles, nerves, and vessels. The thoracic vertebrae can also be typical or atypical. Key joints include the sternocostal joints and costovertebral joints. Intercostal nerves branch and innervate the chest wall. The azygos and hemiazygos veins drain the posterior chest wall.

1. Bones of the thoracic wall
(1) Sternum
(2) Ribs (12 pairs)
(3) Vertebrae (thoracic)
Sternum
It is a flat bone which lies in the midline of anterior chest wall.
Parts
Manubrium sterni, It Lies opposite T3,T4.
Body, It lies opposite to T5 to T8.
Xiphoid process, T9.
The manubrium has the facet for the first costal cartilages and a
facet for the clavicle. The facet for second costal cartilage occur at
the sternal angle. The remaining costal cartilages fuses at sternal
body.

2. On the basis of structure the ribs are of two types
(1) Typical rib
It is a long, twisted, flat bone having a rounded, smooth superior
border and a sharp, thin inferior border. The inferior border overhangs
(extend outwards) and forms the costal groove, which accommodates the
intercostal vessels and nerve.
The anterior end of each typical rib is attached to the corresponding costal
cartilage.
It has a head, neck, tubercle, shaft, and angle. The head has two facets for
articulation with the vertebral body.
The neck is a constricted portion situated between the head and the tubercle.
The tubercle is a prominence on the outer surface of the rib at the junction of
the neck with the shaft.
The shaft is thin and flattened and twisted on its long axis. Its inferior border
has the costal groove. The angle is where the shaft of the rib bends sharply
forward.

3. (2) Atypical ribs
Some ribs varies in structure than the typical ribs which are
called atypical ribs.
The 1st rib is an example of atypical rib. It is important clinically
because of its close relationship to the lower nerves of the
brachial plexus and the main vessels to the arm, namely, the
subclavian artery and vein. This rib is small and flattened from
above downward. The scalenus (of a triangle or having sides
unequal in length) anterior muscle is attached to its upper
surface and inner border. Anterior to the scalenus anterior, the
subclavian vein crosses the rib, posterior to the muscle
attachment, the subclavian artery and the lower trunk of the
brachial plexus cross the rib and lie in contact with the bone.

4. Costal Cartilages
Costal cartilages are bars (Rod) of cartilage
connecting the upper seven ribs to the lateral edge
of the sternum and the 8th, 9th, and 10th ribs to the
cartilage immediately above. The cartilages of the
11th and 12th ribs end in the abdominal
musculature.
The costal cartilages contribute significantly to the
elasticity and mobility of the thoracic walls. In old
age, the costal cartilages tend to lose some of their
flexibility as the result of superficial calcification

5. Intercostal Spaces
The space between two adjacent ribs is called intercostal space.
There are 9 anterior and 11 posterior intercostal spaces.
Each space contains:
1- Intercostal muscles: External, Internal and innermost.
2- An Intercostal nerve.
3- Intercostal vessels:
a. Intercostal arteries Anterior & Posterior.
b. Intercostal veins Anterior & Posterior.
The intercostal nerves, veins and arteries runs near the lower border of the rib in the following
manner from above below,
Vein, Artery and Nerve (VAN). The innermost intercostal muscles are covered by endothoracic
fascia, which is lined internally by the parietal pleura.

6. Thoracic vertebrae
It makes the axial part of the poster chest
wall. They are 12 in number. The thoracic
vertebrae may be typical and atypical. The typical
thoracic vertebrae has structure of a common
vertebrae while the structure of atypical
vertebrae is somewhat changed from the typical.

7. 1st, 10th,11th and 12th
T1
Has a complete facet.
One very small inferior demifacet(actually half of a facet).
Spine nearly horizontal has costal facet in transverse process for the tubercle of first rib.
It has a small body, looks like a cervical vertebra.
T10
One complete facet with the upper border
Small costal facet on transverse process.
T11
One complete circular facet away from upper border.
No costal facet
T12
Broad body & short, oblong spine.
One complete facet midway between upper & lower borders.
No costal facet
Atypical (Non typical ) thoracic vertebrae.

8. Joints of the thoracic wall
Joints of the Sternum
Manubriosternal joint Between the manubrium and the body of the
sternum.
Xiphisternal joint
Between xiphoid process and the body of the sternum.
Joints of the Ribs and Costal Cartilages
These joints are cartilaginous joints.
No movement is possible.

9. Joints of the Costal Cartilages with the Sternum
The 1st costal cartilages articulate with the manubrium through
cartilaginous joints.
The 2nd to 7th costal cartilages articulate with the lateral border
of the sternum by synovial joints.
In addition, the 6th, 7th, 8th, 9th, and 10th costal cartilages
articulate with one another along their borders by small synovial
joints.
The cartilages of the 11th and 12th ribs are embedded in the
abdominal musculature.

10. Joints of the Heads of the Ribs
The 1st rib and the three lowest ribs have a single synovial
joint with their corresponding vertebral body.
For the 2nd to 9th ribs, the head articulates by means of a synovial
joint with the corresponding vertebral body and that of the
vertebra above it.
Joints of the Tubercles of the Ribs
The tubercle of a rib articulates by means of a synovial joint with
the transverse process of the corresponding vertebra. This joint is
absent on the 11th and 12th ribs.

11. Intercostal Arteries
Anterior
Each intercostal artery gives off branches to
the muscles, skin and parietal pleura.
In the region of the breast in the female, the
branches to the superficial structures are
particularly large.

12. Posterior intercostal artery
Each intercostal space contains a large
single posterior intercostal artery and
two small anterior intercostal arteries.

13. Intercostal Veins
2 in each space.
(1) Posterior intercostal veins
It drain backward into the
azygos or hemiazygos veins .
And
(2) Anterior intercostal veins
It drain forward into the
internal thoracic and the
musculophrenic veins.

14. Azygos vein
The azygos vein in right side transports
deoxygenated blood from the posterior
walls of the thorax and abdomen into the
superior vena cava vein.
Hemiazygos vein
The hemiazygos vein (vena azygos minor
inferior) is a vein running superiorly in the
lower thoracic region, just to the left side
of the vertebral column

16. Intercostal nerves
They are the anterior branches of spinal thoracic
nerves fromT1 to T11.
Each nerve runs in the Intercostal space inferior to the
Intercostal vessels.
T3 toT6 are called Typical
T12 is called Subcostal(below)
The remaining nerves are called atypical.
These nerves arises from the vertebrae and runs between
the inner and innermost muscles of the intercostal space.

18. Branches of intercostal nerves
Rami communicantes
It connect the intercostal nerve to a ganglion(sac like swelling) of the sympathetic(expressing) trunk.
Gray ramus
It joins the nerve medial at the point at which the white ramus leaves it.
Collateral branch
It runs forward inferiorly to the main nerve on the upper border of the rib below.
lateral cutaneous branch
It reaches the skin on the side of the chest. It divides into an anterior and a posterior branch.
Anterior cutaneous branch
It is the terminal portion of the main trunk. It reaches the skin near the midline.
Muscular branches
These runs to the intercostal muscles.
Pleural sensory branches
These branches goes to the parietal pleura.
Peritoneal sensory branches (7th to 11th intercostal nerves only) they run to the parietal peritoneum.

19. Suprapleural Membrane (Sibson
fascia)
On either side of the structures passing through
the thoracic outlet, a dense fascial layer called the
suprapleural membrane is present.
It is a fibrous sheet and attached laterally to the
medial border of the 1st rib and costal cartilage.
It is attached at its apex to the tip of the transverse
process of the seventh cervical vertebra and medially to
the fascia investing the structures passing from the
thorax into the neck.
It protects the underlying cervical pleura and resists the
changes in intrathoracic pressure occurring during
respiratory movements.