Thorax
•
•
Location: between neck and abdomen
Skeleton
o Thoracic cage (thoracic skeleton)
✓ Horizontal: ribs and costal cartilages
✓ Vertical: sternum (anteriorly) and thoracic vertebrae (posteriorly)
✓ Floor: thoracic diaphragm is invaginated inferiorly (i.e. pushed upward) by viscera of
abdominal cavity
• Components (3 major spaces)
o Mediastinum: lodges thoracic viscera, except the lungs
o R & L pulmonary cavities: contain the lungs
Thoracic wall
•
Components
o Thoracic cage
o Muscles between ribs
o Skin, subcutaneous tissue, muscles, and fascia covering the anterolateral aspect
• Thoracic cage:
o Function:
✓ Provide rigidity, but is very light
✓ Protects thoracic and abdominal organs from external forces
✓ Resists negative internal pressures generated by lungs and inspiratory movements
✓ Attachment and support weight of upper limbs
✓ Attachment for muscles of the upper limbs, abdomen, neck, back, and respiration
• Components of the thoracic skeleton
o 12 ribs and associated costal cartilages
o 12 thoracic vertebrae
o Sternum
Skeleton of thoracic wall
•
Ribs
o Form most of thoracic cage
o Very light weight, but resilient
o Connected to vertebral bodies posteriorly and sternum
anteriorly, except floating ribs
o Types:
✓ True (1st – 7th): attach directly to sternum through
their own costal cartilages
✓ False (8th – 10th): attach indirectly to the sternum
through the costal cartilage of the rib above them
✓ Floating (11th & 12th): do not connect to the sternum
and end in the posterior abdominal musculature
•
Typical ribs (3rd – 9th)
o Head: contains 2 faces separated by
the crest of the head, one articulates
with numerically corresponding
thoracic vertebra and one for the
supra-adjacent vertebra
o Neck: connects head to the body at the
level of the tubercle
o Tubercle: at the junction of neck and
body, articulates with transverse
process of corresponding vertebra
o Body: thin, flat, and curved
✓ Costal angle: where ribs turn
anterolateral
✓ Costal groove: on the internal
surface of body, protects the
intercostal nerve and vessels
•
Atypical ribs (1st, 2nd, and 11th – 12th)
o 1st
✓ Broadest, shortest, and most sharply curved
✓ Single facet on head for articulation with T1
✓ 2 grooves on superior surface for subclavian vessels
✓ Scalene tubercle: attachment for ASM (Anterior Scalene Muscle) and separates the
subclavian grooves
nd
o 2
✓ Tuberosity for serratus anterior muscle
o 11th – 12th
✓ Single facet
✓ No neck
✓ No tubercle
•
Costal cartilages and spaces
o Costal cartilages
✓ Prolong ribs anteriorly, connecting them to the sternum
✓ Contribute to elasticity of thoracic wall
o Costal margin: inferior edge of thorax, formed by the attachment of the 8th – 10th costal
cartilages to the 7th costal cartilage
o Intercostal spaces: space between ribs and their cartilages, named accordingly to the rib forming
the superior border. Contain muscles and membranes, and intercostal nerves and vessels
o Subcostal space: space below the 12th rib. Subcostal nerve is the anterior ramus of spinal nerve
T12
•
Thoracic vertebrae
o General features:
✓ Have bodies
✓ Vertebral arches
✓ Seven processes for muscular and articular
connections
o Characteristic features
✓ Costal facets (bilateral demifacets): articulate with
head of ribs, usually occur in superior and inferior
pairs
✓ Transverse costal facets: articulate with tubercles of
ribs
✓ Spinous processes: long and sloped inferiorly
•
Sternum
o Flat and elongated, forms anterior part of thoracic
cage
o Protects mediastinal viscera, particularly the heart
o Parts:
✓ Manubrium
➢ Jugular notch: concave center of the
superior border
➢ Clavicular notches: on the side, receive
clavicles and form sternoclavicular joints
➢ Sternal angle: manubriosternal joint
✓ Body: located at the level of T5 – T9
✓ Xiphoid process: inferior end at the level of
T10
➢ Xiphisternal joint: indicates inferior
median limit of thoracic cavity
➢ Marker for: superior limit of liver, central
tendon of diaphragm, and inferior border
of heart (locator for cardiac compression)
o Clinical relevance: sternal biopsy is used to obtain bone marrow specimens for marrow
transplantation and for detection of metastatic cancer and blood dyscrasias (abnormalities)
Thoracic apertures
•
Superior thoracic aperture: sloped
anteriorly
o Boundaries: P: T1 vertebra; L:
1st pair of ribs and costal
cartilages; A: superior border of
manubrium
o Content: trachea, esophagus,
nerves and vessels supplying
and draining the head, neck,
and upper limbs
• Inferior thoracic aperture
o Boundaries: P_L: T12 vertebral body and 11th & 12th pair of ribs; A_L: joined costal cartilages of
ribs 7 – 10 forming the costal margin; A: xiphisternal joint
o Content: esophagus, inferior vena cava (pass through the diaphragm). Liver, spleen, and stomach
are protected by the thoracic wall and lie superior to the inferior thoracic aperture
Joints of thoracic wall
•
Intervertebral joints
o IV disks: cartilaginous joints, connecting articulating surfaces of adjacent vertebral bodies
o Ligaments (support)
✓ Anterior longitudinal ligament
✓ Posterior longitudinal ligament
✓ Zygapophysial joints: synovial joint between superior and inferior articular processes of
adjacent vertebrae.
o Ligaments (accessory ligaments supporting the vertebral arches)
✓ Ligamenta flava
✓ Interspinous ligaments
✓ Supraspinous ligament: connects tips of spinous processes from C7 to sacrum; merge
superiorly with the nuchal ligament
•
Costovertebral joints
o Costovertebral joint: synovial joint between
✓ Head of rib
✓ Superior costal facet of corresponding (same numbered) vertebra
✓ Inferior costal facet of vertebra superior to rib
✓ Adjacent IV disk
o Ligaments
✓ Radiate ligament of head of rib: from head of rib to sides of vertebral bodies associated with
it
✓ Intra-articular ligament of head of rib: from head to IV disk
o Costotransverse joints: synovial joints between
✓ Tubercle of rib
✓ Transverse costal facet of corresponding (same numbered) vertebra
o Ligaments
✓ Costotransverse ligament: from neck of rib to transverse process of vertebra
✓ Lateral costotransverse ligament: from tubercle of rib to tip of transverse process
✓ Superior costotransverse ligament: from neck of rib to transverse process of adjacent
superior vertebra
•
Sternocostal joints
o Sternocostal joint: synovial joint between
✓ Costal cartilage of ribs 2 – 7.
➢ costal cartilage of 1st rib forms a
synchondrosis with manubrium (no
synovial capsule)
✓ Sternum
o Ligaments
✓ Radiate sternocostal ligament: from costal
cartilages to the sternum anteriorly and
posteriorly
Fascia of the thoracic Wall
•
Fascia
o Pectoral fascia: deep fascia associated with the pectoralis muscle overlying the anterior thoracic
wall. Forms 2/3 of the breast bed
o Clavipectoral fascia: deep fascia suspended from the clavicle and investing the pectoralis minor
muscle
o Endothoracic fascia: thin fibroareolar lining the thoracic cavity internally.
o It attaches the lining of lung cavities to the thoracic wall
✓ Suprapleural membrane (Sibson fascia): over the apices of the lung
Musculature & Innervation of the Thoracic Wall
•
External intercostal muscles
o 11 pairs in the intercostal spaces (run inferoanteriorly). Deep to serratus anterior muscle
o Extend from rib tubercles to costochondral junctions.
➢ External intercostal membrane: replaces EIM (external intercostal muscle) anteriorly
o F: elevate ribs during forced inspiration
o I: intercostal nerve
• Internal intercostal muscles
o 11 pairs in the intercostal spaces (run inferoposterioly). Deep to external intercostal muscles
o Extend from sternum to angle of ribs.
➢ Internal intercostal membrane: replaces the IIM posteriorly
o F: depress ribs during forced expiration
o I: intercostal nerve
• Innermost intercostal muscles
o 11 pairs, similar to internal intercostal muscles
o Between innermost and internal intercostal muscles is the neurovascular bundle of intercostal
nerves and vessels
• Transversus thoracis muscles
o Extend superolateral from posterior surface of inferior sternum to internal surface of costal
cartilages 2 – 6
o Continuous with the transversus abdominis muscles
•
Diaphragm
o Function:
➢ Main muscle of inspiration. When the fibers contract, they pull the central tendon inferiorly
(down) expanding the thoracic cavity, and increasing lung size. Additionally, it leads to the
compression of abdominal content  good for defecation, micturition, and parturition
o Structure:
➢ Double-domed broad muscle. Central portion is slightly depressed by the pericardium
(contains heart). R dome is higher (liver) than L dome (stomach)
➢ Superior surface is convex and faces the thoracic (floor) cavity, inferior surface is concave
and faces the abdominal (ceiling) cavity
o Muscular fibers radiate from the periphery towards the central tendon and are divided in three
parts
➢ Sternal: attach anteriorly to the xiphoid process
➢ Costal: attach to internal surface of inferior 6 costal cartilages and ribs. Forms the R & L
domes
➢ Lumbar: attach to medial and lateral arcuate ligaments (aponeurotic arches) and the three
superior lumbar vertebrae
o Ligaments
➢ Lateral arcuate ligament: thickening of fascia covering the quadratus lumborum muscle
➢ Medial arcuate ligament: thickening of fascia covering the psoas major muscle
➢ Median arcuate ligament: joins the R & L crura and forms the aortic hiatus
➢ Crura of the diaphragm: musculotendinous bands arising from the superior 3 or 4 lumbar
vertebral bodies (L1 – L3 or L4), the anterior longitudinal ligament, and the IV disks
▪ Right (L1 – L3 or L4) goes around the esophagus to form the esophageal hiatus. Left
crus (L1 – L3)
o
Apertures (openings, hiatus)
➢ Allow passage of structures between thorax and abdomen
➢ Caval opening: aperture in the central tendon of the diaphragm, at the level of T8 – T9.
Transmits the inferior vena cava (IVC) and right phrenic n. It widens during inspiration,
dilating the IVC and facilitating venous return to the heart
➢ Esophageal hiatus: extension of right crus at the level of T10. Transmits the esophagus and
Vagus n.
➢ Aortic hiatus: opening posterior to the diaphragm formed by the R & L crura and the
median arcuate ligament. Transmits the aorta, thoracic duct, and azygos/hemiazygos
venous system
o
Vasculature
➢ Arteries: supply the superior (thoracic) and inferior surfaces (abdominal)
▪ Superior surface (thoracic)
❖ Pericardiacophrenic a.: branches of the internal thoracic a.
❖ Musculophrenic a.: branches of the internal thoracic a.
❖ Superior phrenic a.: branches of the thoracic aorta
▪ Inferior surface (abdominal)
❖ Inferior phrenic a.: branches of the abdominal aorta
➢ Veins:
▪ Superior surface (thoracic)
❖ Pericardiacophrenic v.: drain into internal thoracic v.
❖ Musculophrenic v.: drain into internal thoracic v.
❖ Superior phrenic v.: drain into internal thoracic v.
▪ Inferior surface (abdominal)
❖ Inferior phrenic vv.: drain into the IVC