Thorax Region of the body between

the neck and abdomen Flattened in front and behind,

but rounded on the sides The bony framework of the

walls is called the thoracic thoracic cagecage, which is formed of: Vertebral column

posteriorly Ribs & intercostal spaces

on the sides Sternum and costal

cartilages anteriorly

• Superiorly: It communicates with the neck through an opening bounded: Posteriorly by 1st thoracic

vertebra Laterally by medial border of

the 1st ribs and their costal cartilages

Anteriorly by superior border of manubrium sterni

• This opening is occupied: In the midline, by the structures

that pass between the neck and the thorax

On either sides, it is closed by a dense suprapleural membrane

1

1st rib

Suprapleural membrane

Suprapleural Membrane Tent shaped dense fascial sheet that

covers the apex of each lung. An extension of the endothoracic

fascia Extends approximately an inch

superior to the superior thoracic aperture

It is attached:Laterally to the internal border of

the first rib & costal cartilageAt its apex to the transverse

process of C7 vertebra. Medially to the fascia covering the

structures passing through the superior thoracic aperture

• Inferiorly: It communictes with the abdomen through a large opening bounded: Posteriorly by the 12th

thoracic vertebra Laterally by curving

costal margin Anteriorly by xiphisternal

joint• This opening is closed

by the diaphragm

Costal margin

2th rib

12

• The thoracic cage: Protects the lungs, heart

and large vessels Provides attachment to

the muscles of thorax, upper limb, abdomen & back

• The cavity of thorax is divided into:• A median partition, the

mediastinum• Laterally placed pleurae &

lungs

Cutaneous Nerves• Anterior wall:

Above the level of sternal angle: Supraclavicular nerves

Below the level of sternal angle: Segmental innervation by anterior and lateral cutaneous branches of the intercostal nerves

• Posterior wall: Segmental innervation by

posterior rami of the thoracic spinal nerves nerves

Thoracic Dermatomes

The Intercostal Space

Intercostal Space

• It is the space between two ribs• Since there are 12 ribs on each side,

there are 11 intercostal spaces. • Each space contains:

Intercostal muscles Intercostal neurovascular bundle Lymphatics

Intercostal muscles• Each intercostal space

has three muscles:• External Intercostal• Internal Intercostal• Innermost Intercostal

• Supplied by corresponding intercostal nerves

• Action: • Tend to pull the ribs

nearer to each other Strengthen the tissue

of the space

External Intercostal Muscle• Most superficial• Fibers directed downward &

forward• OriginOrigin: from lower border of the

rib above• InsertionInsertion: upper border of rib

below• Extends from the rib tubercle

behind to the costo-chondral junction in front

• Deficient anteriorly & replaced by external (anterior) intercostal external (anterior) intercostal membranemembrane

Costo-chondral junction

Internal Intercostal Muscle• Intermediate layer• Fibers directed downward &

backward• OriginOrigin: from subcostal groove

of the rib above• InsertionInsertion: upper border of rib

below• Extends from the sternum in

front to the angle of the rib behind

• Deficient posteriorly & replaced by internal (posterior) internal (posterior) intercostal membraneintercostal membrane

S

costochondral junction

CC

V

anterior intercostal membrane &

external intercostal muscle

posterior intercostal membrane &

internal intercostal muscle

Angle of the rib

Innermost Intercostal Muscle• Deepest layer• Incomplete layer,

divided into three portions

• Fibers cross more than one intercostal space

• Related externally to intercostal nerve and vessels, and internally to endothoracic fasciaendothoracic fascia

Endothoracic Fascia• It is the extrapleural fascia

that lines the wall of the chest • It is located between the

muscles and bones of the thoracic wall and the parietal pleura, extends over the apex (cupola) of the pleura as the suprapleural membrane, and forms a thin layer between the diaphragm and the pleura.

Intercostal Neurovascular Bundle• Lies between the innermost and

the internal intercostal muscles• Runs high in the intercostal

space, related to subcostal groove of the rib above

• Has a strict order in arrangement: Vein-Artery-Nerve (VANVAN)), from top to bottom

• As the innermost intercostal muscle is not forming a complete layer, the bundle is generally covered on the inside by the endothoracic fascia

Intercostal Nerves• Twelve pairs• Are the anterior primary anterior primary

rami rami of the thoracic spinal thoracic spinal nerves.nerves.

• 1-6 distributed in the intercostal spaces, 7-11th supply the anterior abdominal wall

• Anterior ramus of 1212thth nerve runs forward in the abdomen as the subcostal nervesubcostal nerve

Intercostal Nerves cont’d• These are mixedmixed nerves & supply the:

• The skin• Muscles of the intercostal space & abdomen • The parietal pleura & parietal peritoneum

• Branches:

• Rami communicantes• Collateral branches Lateral cutaneous Anterior cutaneous Muscular branches Pleural Peritoneal (7th-11th)

Atypical Intercostal Nerves• First thoracic nerve:

• Has no anterior cutaneous branch

• Is joined to the brachial plexus by a large branch that corresponds to the lateral cutaneous branch

• Second thoracic nerve : • Is joined to the medial

cutaneous nerve of the arm by brachial plexus by a branch called the intercostobrachial nerve that corresponds to the lateral cutaneous branch

Intercostal Arteries

• Each intercostal space contains: A single posterior & Two anterior intercostal arteries

• Each artery gives off branches to the muscles, skin, parietal pleura (& breast)

Posterior Intercostal Arteries• In the upper two two spaces,

arise from the superior superior intercostal arteryintercostal artery (a branch of costocervical trunk of the subclavian artery)

• In the lower nine nine spaces, arise from the branches of thoracic aortathoracic aorta

• The course and The course and branching of the branching of the intercostal arteries intercostal arteries follow the intercostal follow the intercostal nervesnerves

Anterior Intercostal Arteries• In the upper sixsix

spaces, arise from the internal thoracic internal thoracic artery artery

• In the lower fivefive spaces arise from the musculophrenicmusculophrenic artery (one of the terminal branch of internal thoracic)

• Form anastomosis with the posterior intercostal arteries

Intercostal Veins• Accompany intercostal

arteries and nerves• Each space has posterior &

anterior intercostal veins• Eleven posterior intercostal

and one subcostal vein• Lie deepest in the costal

grooves• Contain valves which direct

the blood posteriorly

Posterior Intercostal Veins• On right side:On right side:

• The firstfirst space drains into the right brachiocephalic vein

• Rest of the intercostal spaces drain into the azygos vein

• On left side:On left side:• The upper three upper three spaces

drain into the left brachiocephalic vein.

• Rest of the intercostal spaces drain into the hemiazygos and accessory hemiazygos veins, which drain into the azygos vein

Anterior Intercostal Veins

• The lower fivefive spaces drain into the musculophrenicmusculophrenic vein (one of the tributary of internal thoracic vein)

• The upper sixsix spaces drain into the internal internal thoracic veinthoracic vein

• The internal thoracic internal thoracic

vein drains into the subclavian vein.

Lymphatics

• Lymph vessels of the intercostal space conform to the general rule, that deep lymphatics follow arteries• Anteriorly drain into anterior intercostal anterior intercostal

nodesnodes that lie along the internal thoracic artery

• Posterioly drain into posterior intercostal posterior intercostal nodesnodes that lie in the posterior mediastinum

Applied Anatomy Sternum:

used for marrow biopsy May be split to make surgical access to heart, great

vessels and thymus Sternal angle as an important landmark for counting

ribs, costal cartilages and intercostal spaces Thoracic outlet syndrome: Compression of nerves

/vessels at the superior aperture of thorax Cervical rib Referred pain: Disease in the thorax may reveal pain in

the anterior abdominal wall… Why?

Applied Anatomy cont’d

Traumatic injuries to the thorax: Fracture of rib is extremely painful condition as

periosteum of the rib is supplied by the intercostal nerves above & below the rib

Fractured rib may penetrate the lung (and produce pneumothorax) or may damage the upper abdominal organs

Injuries involving multiple ribs result in flail chest. The flail segment is sucked in during inspiration and pushed out during expiration

Applied Anatomy cont’d The intercostal spaces are

important access points for: Surgical procedures, e.g.

resection of (part of) the lung Percussion and auscultation of

underlying structures e.g. heart & lung

To obtain a sample of pleural fluid or drain pus/blood from the pleural cavity. The needle/drain is passed through the intercostal space just above the upper border of the rib to avoid the neurovascular bundle .