THORAX THE THORACIC CAGE Boundaries Behind Bodies of

THORAX

THE THORACIC CAGE : Boundaries: Behind: ü Bodies of twelve thoracic vertebra and their intervening discs ü Posterior parts of ribs In front: ü Sternum ü Anterior part of ribs and their costal cartilages

On each side: Twelve ribs Inlet of thorax: It is reniform in shape Outlet: It is closed by the diaphragm

Skeleton of thorax: Ø Thoracic vertebra Ø Ribs Ø Sternum

Thoracic vertebra: q They are 12 in number q They are recognized by the presence of costal facets on sides of the bodies and transverse process Classification: Typical thoracic vertebra: Second to Eight Atypical thoracic vertebra: First, Nine to Twelve

Features of typical thoracic vertebra: Body , Vertebral foramen, Superior articular facets Transverse process & Spinous process

Body: ☻ It is heart shape ☻ Presence of two costal demifacets

Vertebral foramen: ☻ Small and circular in shape ☻ Pedicles are short ☻Lamina are short, thick and broad

The transverse process: ☻ Tips bear oval costal facets

Spinous process: ☻ Long and slopes downward

Sternum: Consists of three parts ☻Manubrium ☻Body ☻Xiphoid process

Manubrium:

Body:

Xiphoid process:

THE RIBS: ☻ Arranged in twelve pairs ☻Posteriorly it articulates with the thoracic vertebra ☻Anteriorly joins with the sternum through their respective costal cartilages directly or indirectly

Classification of ribs: ☼True ribs: Upper seven pairs (Vertebrosternal ribs) ☼False ribs: Lower five pairs (Vertebro-chondral ribs) ‡Typical ribs: 3 rd to 9 th ribs ‡Atypical ribs: 1 st, 2 nd, 10 th 11 th and 12 th ribs

Typical ribs: ☻ Sternal end ☻Vertebral end ☻Intervening shaft

Sternal end: ☻ Lower than vertebral end and receives its own costal cartilage

Vertebral end: It includes: - Head - Neck - Tubercle

Shaft: It is thin flat and curved

Applied anatomy: Fracture of ribs: Pneumothorax or Haemothorax

INTERCOSTAL SPACE

Intercostal space: Eleven in number on each side Last two intercostal spaces are open in front

Typical Intercostal • Those spaces intervening between typical ribs and space: traversed by vessels and nerves which are confined to the thoracic wall, are known as typical intercostal space • As such 3 rd , 4 th, 5 th and 6 th intercostal space are typical

Boundaries of typical intercostal space: Above: Lower margin of upper rib and its cartilage Below: Upper margin of the lower rib and its cartilage In front: Lateral border of sternum between the costal notches Behind: Body of corresponding thoracic vertebra

Contents of space: v. Muscles v. Vessels and v Nerves

Muscles: They are arranged in three sheets from outside to inside: ØIntercostalis externus ØIntercostalis intimus

Intercostalis externus:

Intercostalis internus:

Intercostalis intimus: † It occupies middle 2/4 th of typical intercostal space † Intercostal vessels and nerves passes between intercostalis internus and intimus muscle

Intercostal vessels: Arteries: Anterior intercostal arteries In each space the arteries are Posterior intercostal arteries arranged in two groups

Anterior intercostal arteries: Upper six spaces: Internal thoracic artery Lower three spaces: Musculo-phrenic artery

Posterior intercostal arteries: Upper two spaces: Superior intercostal artery Lower nine spaces: Descending thoracic aorta

intercostal veins: In each space the veins are arranged in two groups Anterior intercostal veins Upper six spaces Internal thoracic vein Lower three spaces Musculophrenic vein

Posterior intercostal veins On right side Azygous vein On left side Hemiazygous vein

intercostal Nerve: ɸ They are eleven in number ɸ Each nerve is ventral ramus of a thoracic nerve ɸ Ventral ramus of 1 st thoracic nerve forms lower trunk of brachial plexus ɸ Lateral cutaneous branch of 2 nd intercostal nerve remains as intercostobrachial nerve ɸ 3 rd to 6 th intercostal nerves are called as typical intercostal nerves ɸ 7 th to 11 th intercostal nerves appears in anterior abdominal wall

Branches: † Rami communicantes † Collateral branch † Lateral cutaneous branch † Muscular branches run to the intercostal muscles. † Pleural sensory branches go to the parietal pleura. † Peritoneal sensory branches (7 th to 11 th intercostal nerves only) run to the parietal peritoneum

Applied anatomy: Intercostal neuralgia: It is a sharp burning pain in the area of skin supplied by thoracic spinal nerve produced by rib fracture Herpes zoster Caused by a virus called as varicella-zoster virus