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Name the intercostal muscles

1. External intercostal
2. Internal intercostal
3. Transversus thoracis - subcostalis + intercostalis intimi + sternocostalis


Extent of external intercostal muscles

-From tubercle of rib posteriorly to costochondral junction anteriorly
-Between costochondral junction to sternum replaced by external intercostal membrane
-Posterior part continuous with superior costotransverse ligament
-Fibres run downwards, forwards and medially


Extent of the internal intercostal muscles

-From lateral border of sternum to angle of rib
-Continues as internal intercostal membrane which is continuous with superior costotransverse ligament
-Fibres run downwards, backwards and laterally


Extent of transversus thoracis muscle

Subcostalis - Posterior part of lower intercostal spaces
Intercostalis intimi - Middle 2/3rds of all spaces
Sternocostalis - Anterior parts of upper spaces


Intercostal nerves distribution

-They are ventral primary rami of T1-T11 spinal N
-All supply intercostal spaces
-Upper 2 also supply upper limb
-Lower 5 also supply abdominal wall
-3-6 Typical intercostal N


Intercostal N relations

-Passes below neck of rib and enters costal groove
-Posterior part: between pleura and internal intercostal membrane
-Anterior part: between intercostalis intimi and internal intercostal muscle
-In the front, pierces intercostal muscles and forms ANTERIOR CUTANEOUS N


Muscular branches of intercostal N

1. Supply intercostal muscles, serratus posterior superior
2. Collateral branch arises near angle of rib and supplies neurovascular space


Sensory branches of intercostal N

1. Main and collateral branch supply pleura and periosteum
2. Lateral cutaneous branch near angle of rib supplies skin
3. Anterior cutaneous branch near sternum supplies skin


Intercostobrachial N

-It is the lateral cutaneous branch of 2nd intercostal N.
-Supplies skin of floor of axilla and upper medial part of arm


Boundaries of typical intercostal space

Superior: Costal groove of rib above
Inferior: Upper border of rib below
Anterior: Sternum
Posterior: Thoracic vertebra


Contents of typical intercostal space

1. Intercostal muscles
2. 2 anterior intercostal A and V
3. Posterior intercostal A and V
4. Intercostal N and collateral branch


Origin of posterior intercostal A

1-2: superior intercostal A -> costocervical trunk -> subclavian A
3-11: descending thoracic aorta


Course of posterior intercostal A

1. - Right A pass behind esophagus, thoracic duct, azygos vein and sympathetic chain
- Left A pass behind hemiazygos vein and sympathetic chain

2. In intercostal space, intercostal V and N are present above and below resp.

3. Ends at costochondral unction by anastamosing with upper anterior intercostal A


Branches of intercostal A

1. Dorsal: to skin of back and vertebrae
2. Collateral: anastamoses with lower anterior intercostal A
3. Muscular: to intercostal muscles, pectoral, serratus anterior
4. Lateral cutaneous: accompanies LCN
5. Mammary: from 2,3,4 to mammary gland
6. Right bronchial: from 3rd right PIA


Anterior intercostal A

1. 2 in each space: upper and lower
2. 1-6 from internal thoracic A
3. 7-9: from musculophrenic A
4. End at costochondral junction


Anterior intercostal V

1. 1-3 drain into internal thoracic V
2. 4-6 into vena comitantes of internal thoracic A
3. 7-9 into vena comitantes of muculophrenic A


Posterior intercostal V on left side

1- Left brachiocephalic
2,3,4- Superior intercostal -> left brachiocephalic
5-8 - Accessory hemiazygos
9-11 - Hemiazygos


Posterior intercostal V on right side

1- Right brachiocephalic
2,3,4 - Superior intercostal -> azygos
5-11 - Azygos


Relations of internal thoracic A

It runs behind
1. Sternal end of clavicle
2. Internal jugular V
3. Brachiocephalic V
4. 1st costal cartilage
5. Phrenic N

1. Pectoralis major
2. 1-6 costal cartilages
3. External intercostal membranes
4. Internal intercostal muscles
5. 1-6 intercostal N

1. Endothoracic fascia
2. Pleura
3. Sternocostalis


Branches of internal thoracic A

1. Pericardiacophrenic: to pericardium and pleura
2. Mediastinal: to thymus, mediastinum fat
3. 2 anterior intercostal A at each space
4. Superior epigastric A: enters rectus sheath
5. Musculophrenic A: runs behind 7,8,9 costal cartilages and gives 2 intercostal branches at each space. Perforates diaphragm near 9th CC


Formation of azygos V

-Union of:
1. Lumbar azygos
2. Right subcostal
3. Ascending lumbar
-Occupies posterior medistinum and joins superior vena cava
-Enters thorax by passing through aortic opening


Relations of azygos V

Anteriorly: Oesophagus
Posteriorly: Thoracic vertebrae, Right posterior intercostal V
Right: Right lung, pleura
Left: Thoracic duct, Aorta, Trachea, Vagus


Tributaries of azygos V

1. Right superior intercostal V
2. 5-11 right posterior intercostal V
3. Hemiazygos V
4. Accessory hemiazygos V
5. Right bronchial V


Hemiazygos V

-Formed by union of:
1. Left lumbar azygos
2. Left ascending lumbar
3. Left subcostal
-Pierces crus of diaphragm, ascends on left side of vertebra, overlapped by aorta, joins azygos
-Gives 9-12 left posterior intercostal V


Accessory hemiazygos V

-Begins in 4/5th intercostal space
-At level of 8th space, turns right, passes behind aorta and thoracic duct and joins azygos
-Gives 5-8 left posterior intercostal V


Branches of thoracic sympathetic trunk

-Grey rami communicans supply skin

1. Upper 5-pulmonary, cardiac, aortic an doesophageal branches
2.Lower 7-Greater, Lesser and least splanchnic N


Greater splanchnic N

-ends in coelic ganglio, aorticorenal ganglion, suprarenal gland


Lesser splanchnic N

-Coeliac ganglion