Thoracic Cage
- The thoracic cage consists of the sternum, the ribs, and the
thoracic vertebrae.
- It has a narrow inlet and a wide outlet.
I. Thoracic inlet: (the upper opening of the thoracic cage)
Boundaries:
a. Anterior -------------- Supra-sternal notch of the
manubrium sterni.
b. On each side --------- First rib.
c. Posterior -------------- First thoracic vertebra.
Ribs
Classification of ribs according to their attachments to
the sternum:
- There are twelve ribs on each side classified as:
A: True ribs --------- Upper seven ribs (their anterior end is
attached to the sternum).
B: False ribs --------- Lower five ribs (they are not attached
anteriorly to the sternum).
- The lower two ribs are called the floating ribs because
they are free anteriorly.
Classification of ribs according to their structure:
A: Typical ----------- 3rd - 9th ribs.
B: Atypical ---------- 1st, 2nd, 10th, 11th, and 12th ribs. (first
two and last 3) ribs)
Typical rib
Typical thoracic vertebra
Lateral
surface
Superior
surface
It contains:
1- Intercostal muscles.
2- Intercostal nerves.
3- Intercostal arteries.
4- Intercostal veins.
Intercostal muscles
I. Outer layer ----- External intercostal muscle
II. Intermediate layer ----- Internal intercostal
muscle
III. Inner layer ----- Transversus thoracis group,
subdivided into:
1. Innermost inter-costalis
2. Sterno-costalis
3. Sub-costalis
Intercostal Muscles
Lateral view
Transversus thoracis group
Arrangements and extension of the muscles
Sub Costalis muscle in the
posterior part of the wall
Intercostal Arteries
Intercostal Arteries:
1- Anterior Intercostal Arteries.
2- Posterior Intercostal Arteries.
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Anterior Intercostal Arteries
Each anterior intercostal space
contains two anterior
intercostal arteries (except in
the lower two inter-costal
spaces).
a. The upper 6 pairs arise from
the internal thoracic artery.
b. The 7th, 8th, and 9th pairs
arise from the musculophrenic artery.
Internal thoracic (mammary)
artery
Origin: From the first
part of the subclavian
artery.
Termination: opposite
the sixth intercostal
space by dividing into
superior epigastric
and musculo-phrenic
arteries.
a
Branches:
1. Pericardial branches.
2. Pericardiaco-phrenic
artery.
3. Mediastinal branches.
4. Sternal branches.
5. Perforating branches for
the mammary gland.
6. Anterior intercostal
arteries (upper 6 spaces).
7. Superior epigastric artery.
8. Musculo-phrenic artery.
Internal thoracic (mammary) vein
- It is formed by the
union of the two venae
comitantes of the
internal thoracic artery
behind the third costal
cartilage.
- It ascends close to the
artery to terminate in
the corresponding
innominate vein.
Posterior Intercostal Arteries
- Each posterior intercostal space
contains one posterior intercostal
artery which runs in the costal
groove .
- Each artery gives a collateral branch
which runs over the upper border of
the rib below.
*The upper two posterior intercostal
arteries superior intercostal
artery (from the costo-cervical
trunk)  2nd part of subclavian
artery.
* From 3 - 11 posterior intercostal
arteries and subcostal artery 
descending thoracic aorta.
Intercostal Nerves
- There are 11 intercostal nerves in the upper 11
intercostal spaces and a subcostal nerve below the last
rib (on each side).
- Each intercostal nerve arises from the ventral ramus
of the corresponding thoracic nerve.
- They are classified into:
I. Typical Intercostal Nerves
II. Atypical Intercostal Nerves: which are the
first intercostal nerve, second intercostal nerve and
lower five intercostal nerves .
I. Typical Intercostal Nerves
I. Typical Intercostal Nerves
Branches
1. Communicating branch to the sympathetic trunk.
2. Collateral branch which runs over the upper border of
the rib below.
3. Anterior cutaneous branch .
4. Lateral cutaneous branch which divides into anterior
and posterior branches.
5. Muscular branches to the intercostal muscles.
6. Sensory branches to the pleura.
II. Atypical Intercostal Nerves
1. First intercostal nerve
- It has a small lat. Cut. Branch to the axilla and ends as a
small anterior cutaneous branch.
2. Second intercostal nerve
- Its lateral cutaneous branch is called the intercostobrachial nerve which supplies the base of the axilla and
upper part of the medial side of arm and does not divide
into anterior and posterior branches.
3. Lower five intercostal nerves
- They reach the anterior abdominal wall at the anterior ends
of the spaces and supply its structures in addition to the
diaphragm.
Arrangement of intercostal nerve and
vessels in the costal groove
 In the posterior end of the
space  the nerve is above
the vessels.
 Then, it crosses behind
the vessels to continue
below them (VAN).
 In the posterior part , the
vessels& nerve are midway
between the two ribs.
 In the lateral& anterior
parts  In the costal
groove
Applied anatomy:
1. Stab wounds in the posterior part of the
intercostal spaces lead to injury of the posterior
intercostal nerve and vessels because they run
midway between the ribs.
-But in the lateral part of the intercostal spaces,
they do not injury the posterior intercostal nerve
and vessels because these structures are protected
by the costal groove.
Applied anatomy:
2. Needles introduced into the intercostal
spaces (to remove collection in the pleura)
Site: They are done in the lateral part of the chest
wall to avoid injury of the posterior intercostal
nerve and vessels.
(It is also better to be introduced near the rib
below).
Thank You
Prof.: Dr. Wafaa Abdel-Rahman