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Bones and muscles of the thorax
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Thorax extends from the neck to the abdomen, and includes the primary
organs of the cardiovascular and respiratory systems
Thoracic cavity is cone shaped, with a thin wall (essentially just the skeleton
beneath)
The thoracic cage (rib cage) is formed of ribs and costal cartilage attached
to the sternum ad thoracic vertebrae
Floor of the thoracic cavity is the diaphragm, which is dome-shaped due to
being pushed upward by viscera of the abdominal cavity
Thorax consists of three main spaces: right and left pulmonary cavities
(containing lungs) and mediastinum (containing heart, great vessels, nerves,
oesophagus, trachea etc
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Ribs, costal cartilages and intercostal spaces
Ribs
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Ribs are curved, flat bones forming most of the thoracic cage
Ribs have a spongy interior containing bone marrow
Three types of ribs:
o True (vertebrostinal) ribs 1-7: attach directly to sternum via own
costal cartilage
o False (vertebronchondral) ribs 8, 9 and sometimes 10: cartilage is
attached to the cartilage of the rib superior to them; indirect
connection to sternum
o Floating (vertebral, free) ribs 11 and 12 (sometimes 10): rudimentary
cartilage of these ribs does not connect to sternum or to superior
ribs
Ribs can also be classed as typical or atypical:
o Typical ribs (3-9) have the following features
 Head: wedge-shaped with two facets separated by the
crest of the head; one facet articulates with numerous
corresponding vertebra and the other with the superior rib
 Neck: connects the head of the rib to the tubercle
 Tubercle: junction of head and body; comprises a smooth
articular facet for articulation with transverse process of
vertebra, and rough non-articular part providing attachment
for the costotransverse ligament
 Body (shaft): thin, flat and curved; turns anterolaterally at the
costal angle; concave internal surface has a costal groove
which provides some protection for intercostals nerve and
vessels (order is VAN; located between inner and innermost
intercostals)
o Atypical ribs (1, 2, 10-12) are all different
 Rib 1 is broad, short and most sharply curved of the true ribs;
single facet on head for articulation with the T1 vertebra; two
transverse grooves on superior surface for subclavian vessels;
grooves separated by scalene tubercle and ridge where the
scalene muscle attaches
 Rib 2 is thinner, less curved and longer than rib 1; two facets
for articulation with T1 and T2; rough area on upper surface
(tuberosity for serratus anterior muscle)
 Ribs 10-12 like rib 1 have only one facet on heads and
articulate with a single vertebra
 Ribs 11 and 12 are short with no neck or tubercle

Costal cartilages
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Prolong ribs anteriorly, contribute to elasticity of thoracic wall and provide
flexible attachment
Costal margin: lower edge of the thorax formed from the costal cartilage of
the false ribs 8-10 and true rib 7

Intercostal spaces
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Separate the ribs and costal cartilages from each other; named according to
the rib forming the superior border of the space
Eleven intercostals spaces with 11 intercostal nerves
Spaces are occupied by intercostals muscles and membranes, with two sets
(main and collateral) vessels and nerves
Below rib 12 is the subcostal space; anterior branch of spinal nerve T12 is the
subcostal nerve
Widest anterolaterlally, widen with inspiration, and further widen by
extension/lateral flexion of the thoracic vertebral column on the contralateral
side

Thoracic vertebrae
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Most thoracic vertebrae are independent, have bodies, vertebral arches and
seven processes for muscular and articular attachment
Characteristic features
o Bilateral costal facets (demifacets) on bodies: usually inferior and
superior pairs, articulate with rib heads
 Facets are arranged in pairs with superior and inferior vertebrae,
to form a single socket for a rib head
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head of rib 6 forms socket with superior costal facet of T6
and inferior costal facet of T5
 Atypical thoracic vertebrae have whole costal facets rather
than demifacets; T1 has an inferior costal facet but no superior
costal facet as no corresponding ones on C5 above
 T10 has one bilateral pair of costal facets located on body
 T11 and T12 have single pair of costal facets on pedicle
o Costal facets on transverse process: articulate with rib tubercles; not
present on inferior 2/3 thoracic vertebrae (T11-12 +/- T10)
o Long, inferior slanting spinous processes
 Usually overlap with vertebra below
 Cover intervals between laminae of adjacent vertebrae,
preventing sharp objects from entering the vertebral canal and
damaging the spinal cord
o The inferior articulate processes slope anteriorly
Planes of the articular facets form an arc, centring on an axis of rotation in the
vertebral body; small rotary movements allowed, limited by the rib cage

Taken from Spine and Nerve Anatomy, Chapter 5: Parts of Vertebrae – Thoracic, available at
http://www
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com/Chapter_Fig_folders/Ch05_Anatomy_Folder/5ThoracicVert
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The sternum
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Flat elongated bone in the central anterior part of the thoracic cage
Directly overlies and protects mediastinal viscera and the heart
Consists of three parts: manubrium, body and xiphoid process
o Connected by cartilaginous joints in adolescents and young adults
until ossification in middle to late adulthood

Manubrium
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Trapezoidal shaped bone, widest and thickest part of the sternum
Concave centre of the superior border is the suprasternal/jugular notch
Clavicular notches formed where the clavicles meet (sternoclavicular joints)
Costal cartilage of first rib attaches to the manubrium inferolaterally to the
clavicular notches – synchondrosis of the first rib
Manubriosternal joint is where the manubrium joins the sternum; due to the
angular differences between the manubrium and sternum (manubrium slants
posteriorly, sternum is vertical) this forms a projecting sterna angle (of Louis)

Body of sternum
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Longer, narrower and thinner than the manubrium; located T5-T9 level
Varied width due to costal notches
Four segments (sternebrae) are apparent in young people, separated by
cartilaginous joints; these fuse by age 25 years; three variable transverse
ridges observable in adults where the segments are fused

Xiphoid process
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Smallest and most variable part of the sternum; thin and elongated; end
shape can vary
Inferior end lies at T10 level
Cartilaginous in young people but mostly ossified from age 40 onwards
Important landmark
o Xiphosternal joint indicates inferior limit of the central part of thoracic
wall; also site of the infrasternal angle (angle created by right and left
costal margins)
o Midline marker for superior limit of liver, central tendon of the
diaphragm, inferior border of the heart

Image taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition
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Joints of the thoracic wall
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Range of movement of individual joints is small, but reduced mobility
interferes with breathing
Eight types of thoracic joints:
o Intervertebral: between vertebrae T1-T12, separated by intervertebral
discs
o Costovertebral: between head of ribs and vertebrae
o Costochondrial: between head of rib and costal cartilage
o Interchondrial: between costal cartilages of ribs 6 and 7, 7 and 8, 8 and
9
o Sternocostal: between costal cartilage and sternum
o Sternoclavicular: between sternum and clavicle
o Manubriosternal: manubrium to sternum body
o Xipisternal: xiphoid process to sternum body

Costovertebral joints
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Typical rib articulates with vertebral column at two points; joints of heads of
ribs and costotransverse joints
Joints of heads of ribs
o Head of rib articulates with superior facet of same-numbered vertebra
and inferior facet of the vertebra above, and adjacent intervertebral
disc
o Head of rib attaches to the intervertebral disc via intra-articular
ligament of head and rib
o Head of rib attaches to the bodies of the two vertebrae by radiate
ligament of head of rib
Costotransverse joints

Ligaments lateral to the posterior sides of the vertebrae provide
strength
o Costotransverse ligaments passes from neck of the rib to the transverse
process
o Lateral costotransverse ligament passes from tubercle to tip of
transverse process
o Superior costotransverse ligament is a broad band that joins the crest
of the neck of the rib to the transverse process superior to it; aperture
between the ligament and the vertebra to allow passage of the spinal
nerve and posterior branch of the intercostal artery
o Articular surfaces of ribs 1-6 are convex, allowing rotation around a
transverse axis, allowing elevation and depression in the sagittal plane
o Articular surfaces of ribs 7-10 are flat and articular, allowing gliding;
facilitates elevation and depression in the transverse plane
Sternocostal joints
o Synchondrosis of first rib – joint of rib 1 to manubrium
o Costal cartilages 2-7 articulate with the sternal body
o Joint capsules thickened anteriorly and posteriorly to form radiate
sternocostal ligaments
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Image taken from Moore et al, Clinically Oriented Anatomy, Seventh Edition
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True muscles of the thoracic wall
o Serratus anterior and posterior, levatores costarum, intercostal,
subcostal, and transverses thoracis

Taken from UNMC
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unmc
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Taken from BlogSpot
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blogspot
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uk/2011/03/breathing
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com, Thoracic Wall and Pleura at Vanderbilt University Medical
School, available at https://www
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com/notes/note/n/thoracic-wall-andpleura/deck/4252435

Muscle
Serratus
posterior
superior
Serratus
posterior
inferior
Levator
costarum
External
intercostal
Internal
intercostal
Innermost
intercostal
Subcostal

Origin
Nuchal ligament,
spinous processes of
C7-T3
Spinous process T11-L2

Insertion
Superior border of 2-4
ribs

Innervation
2-5th intercostal
nerves

Action
Proprioception
Elevate ribs

Inferior border 8-12 rib
(angle)

T9-T12 (anterior
rami)

Proprioception
Depress ribs

Transverse process T711
Inferior border ribs

Subadjacent ribs

C8-T11 (posterior
rami)
Intercostal nerve

Elevate ribs

Transversus
thoracis

Sternum

Superior border of rib
below

Elevate rib during forced inspiration
During forced respiration, interosseous
part depresses and interchondrial part
elevates

Lower ribs near angle

Second or third ribs
below
Costal cartilages 2-6

Per internal intercostals
Weak depression
Proprioception

Fascia of the thoracic wall
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Each section of deep fascia is named after the muscle it invests or structure it
attaches to
Pectoral fascia overlays anterior wall, over pectoralis major muscles
Clavipectoral fascia lies deep to pectoralis major and pectoral fascia,
suspended from clavicle and overlaying pectoralis minor
Endothoracic fascia lines the internal surface of the thoracic cage – attaches
costal parietal pleura to thoracic wall
o More fibrous over lung apices (suprapleural membrane)

Nerves of the thoracic wall
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12 pairs of thoracic spinal nerves supply the thoracic wall
Leave the intravertebral foramen and divide into anterior and posterior rami
(branches)
Anterior rami form intercostals nerves; anterior rami of T12 nerve is the
subcostal nerve
Posterior rami pass posteriorly to supply joints, deep back muscles and skin of
the back in the thoracic region

Vasculature of thoracic wall
Arteries
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Arterial supply derives from
o Thoracic aorta, via posterior intercostals and subcostal arteries
o Subclavian artery, via internal thoracic and supreme intercostals
arteries
o Axillary artery, through the superior and lateral thoracic arteries
Intercostal arteries go through thoracic wall between the ribs
o Each intercostals space (bar 10th and 11th) supplied by three arteries –
large posterior and pair of small anterior
Posterior intercostals arteries
o 1st and 2nd intercostals spaces: arise from superior intercostals artery, a
branch of the subclavian artery
o 3-11th intercostals spaces: arise from thoracic aorta
o Pass between internal and innermost intercostals muscles
o Supply intercostals muscles, overlying skin and parietal pleura
Anterior intercostals arteries
o Supply anterior parts of upper 9 intercostal spaces
o Arise from internal thoracic artery (intercostals spaces 1-6) and
musculophrenic arteries (intercostals spaces 7-9)
o Pass between internal intercostals and innermost intercostals
o Supply intercostals muscles, overlying skin and parietal pleura
Internal thoracic arteries

Originate from subclavian artery
Pass inferior and lateral to the sternum, between costal cartilage and
the transversus thoracic muscle – divide into superior epigastric and
masculophrenic arteries
o Supply intercostals spaces 1-6 and (via anterior intercostals) and
musculophrenic artery
Subcostal arteries
o Originate from thoracic aorta
o Courses along border of 12th rib
o Supply muscles of anterolateral abdominal wall
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Taken from Drake et al, Gray’s Anatomy for Students, Second Edition
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Reference
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Clinically Oriented Anatomy
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