Thoracic Wall, Intercostal Muscles

Gross Anatomy

Thoracic Wall, Intercostal Space


Anatomy Tables for Today's Topic

Topographic Anatomy of the Thorax
Bones of the Thoracic Wall
Muscles of the Thoracic Wall
Nerves of the Thoracic Wall
Arteries of the Thoracic Wall
Veins of the Thoracic Wall
Fasciae of the Thorax
Joints of the Thoracic Wall



Topographic Anatomy of the Thorax

Structure/Space Description/Boundaries Significance
midaxillary line an imaginary vertical line passing through the middle of the axilla used as a surface landmark for descriptive purposes
midclavicular line an imaginary vertical line passing through the midshaft of the clavicle used as a surface landmark for descriptive purposes
nipple located superficial to the 4th intercostal space in the male and prepuberal female location of the left nipple may be used to help locate the apex of heart, which is approximately 8 cm from the midline in the left 5th intercostal space; a surface landmark used to place the stethoscope for auscultation of the bicuspid valve
sternal angle a protrusion on the anterior thoracic wall at the junction of the manubrium and body of the sternum (manubriosternal symphysis) sternal angle is the location of the attachment of t the costal cartilage of the 2nd rib to the sternum; an imaginary horizontal plane through the sternal angle passes through the T4/T5 intervertebral disc and marks the inferior boundary of the superior mediastinum
suprasternal notch the notch located at the superior border of the manubrium of the sternum, between the sternal ends of the clavicles also known as: jugular notch
thoracic inlet the opening at the superior end of the rib cage through which cervical structures enter the thorax; bounded by the T1 vertebral body, both of the 1st ribs and their costal cartilages, and the manubrium of the sternum thoracic inlet marks the boundary between the neck and the superior mediastinum; also known as: superior thoracic aperture
thoracic outlet the opening at the inferior end of the rib cage through which thoracic structures exit the thorax; it is bounded by the T12 vertebral body, both 12th ribs, the costal cartilages of ribs 7-12, and the xiphisternal joint thoracic outlet is closed by the respiratory diaphragm which is attached at its boundary; also known as: inferior thoracic aperture

Bones of the Thoracic Wall

Bone Structure Description Notes
rib the bone forming the lateral thoracic wall 12 pairs; several types are described: typical or "true" ribs, "false" ribs, "floating" ribs; all three types of ribs have many features in common: head, neck, tubercle, angle, body, costal groove
head posteromedial end of the rib it articulates with demifacets of two adjacent vertebral bodies
neck the constricted region lateral to the head of the rib the neck of the rib is located between the head and the tubercle
tubercle a projection located posteroinferior and lateral to the neck of the rib it articulates with the transverse process of a vertebra
body the shaft of the rib the body is the longest part of a typical rib
angle the marked angulation of the body located just lateral to the tubercle the angle of the rib is its most posterior part
costal groove the groove on the inner surface of the inferior border of the body of the rib it accommodates the intercostal neurovascular bundle; the costal groove provides a protective function for the intercostal neurovascular bundle,
ribs 1-7 "true" ribs - those which attach directly to the sternum true ribs actually attach to the sternum by means of a costal cartilage and a true synovial joint
rib 1 the most cephalic rib it is the broadest, shortest and widest of the ribs; the scalene tubercle marks its superior surface and is an elevation between grooves for the subclavian vein & artery; the scalene tubercle is the attachment site of the scalenus anterior m.
rib 2 the rib attached to the 1st and 2nd thoracic vertebrae it articulates via a costal cartilage with the sternum at the level of the sternal angle; its superior surface is roughened by the attachments of the scalene mm.
rib 8-10 "false" ribs they articulate via costal cartilages with the costal cartilage of rib 7
rib 11-12 "floating" ribs the anterior ends of these ribs do not articulate with the sternum or the costal cartilage of the rib above; their costal cartilages are short and end in the muscle of the posterolateral abdominal wall
sternum the broad flat bone forming the anterior thoracic wall it is formed by three parts: manubrium, body, xiphoid process
manubrium the superior part of the sternum manubrium means "handle", as in the handle of a sword
jugular (suprasternal) notch a notch on the superior border of the manubrium it is located between the clavicular notches which articulate with the sternal ends of the clavicles
clavicular notch a notch on the superolateral border of the manubrium it articulate with the sternal end of the clavicle
sternal angle the junction of the manubrium and body of the sternum it is an anterior projection located at the level of the costal cartilage of rib 2; an important landmark for internal thoracic anatomy
body the middle part of the sternum it articulates with the manubrium superiorly and the xiphoid process inferiorly; laterally it articulates with the costal cartilages of ribs 2-7
xiphoid process the inferior part of the sternum xiphoid means "sword shaped"; it is variable in size, shape & ossification; it articulates with the body of the sternum superiorly

Muscles of the Thoracic Wall

Muscle Origin Insertion Action Innervation Artery Notes
external intercostal lower border of a rib within an intercostal space upper border of the rib below, coursing, downward and medially keeps the intercostal space from blowing out or sucking in during respiration intercostal nerves (T1-T11) intercostal a. 11 in number; they extend from the tubercle of the rib to the costochondral junction; continuous with the external intercostal membrane anteriorly
innermost intercostal upper borders of a rib fibers course up and medially to insert on the inferior margin of the rib above keeps the intercostal space from blowing out or sucking in during respiration intercostal nerves (T1-T11) intercostal a. innermost intercostal mm. have the same fiber direction as the internal intercostal mm., the only difference being that they lie deep to the intercostal neurovascular bundle
internal intercostal upper border of a rib lower border of rib above, coursing up and medially keeps the intercostal space from blowing out or sucking in during respiration intercostal nerves (T1-T11) intercostal a. 11 in number; they extend from the margin of the sternum to the angle of the rib; continuous posteriorly with the internal intercostal membrane
serratus posterior inferior thoracolumbar fascia, spines of vertebrae T11-T12 and L1-L2 ribs 9-12, lateral to the angles pulls down lower ribs branches of the ventral primary rami of spinal nerves T9-T12 lowest posterior intercostal a., subcostal a., first two lumbar aa. a respiratory muscle, it receives ventral ramus innervation; embryonically related to the intercostal muscles, not the deep back mm.
serratus posterior superior ligamentum nuchae, spines of vertebrae C7 and T1-T3 ribs 1-4, lateral to the angles elevates the upper ribs branches of the ventral primary rami of spinal nerves T1-T4 posterior intercostal aa. 1-4 a respiratory muscle, it receives ventral ramus innervation; embryonically related to the intercostal muscles, not the deep back mm.
subcostalis angle of ribs angle of a rib 2-3 ribs above origin compresses the intercostal spaces intercostal nerves intercostal a. subcostalis, transversus thoracis & innermost intercostal mm. make up the deepest intercostal muscle layer
transversus thoracis posterior surface of the sternum inner surfaces of costal cartilages 2-6 compresses the thorax for forced expiration intercostal nerves 2-6 internal thoracic a. transversus thoracis, subcostalis & innermost intercostal mm. make up the innermost intercostal muscle layer

Nerves of the Thoracic Wall

Nerve Source Branches Motor Sensory Notes
intercostal n. ventral primary rami of spinal nerves T1-T11 lateral & anterior cutaneous brs. intercostal muscles; abdominal wall muscles (via T7-T11); muscles of the forearm and hand (via T1) skin of the chest and abdomen anterolaterally; skin of the medial side of the upper limb (via T1-T2) intercostal n.travels below the posterior intercostal a. in the costal groove
subcostal n. ventral primary ramus of T12 lateral cutaneous br., anterior cutaneous br. muscles of the abdominal wall skin of the anterolateral abdominal wall the subcostal n. is equivalent to a posterior intercostal n. found at higher thoracic levels

Arteries of the Thoracic Wall

ArterySourceBranchesSupplyNotes
epigastric, superior internal thoracic a. no named branches upper rectus abdominis m., upper abdominal wall superior epigastric a. is the direct continuation of the internal thoracic a.; it s anastomoses with the inferior epigastric a. within the rectus abdominis m.
intercostal, anterior internal thoracic a. (upper 6 intercostal spaces), musculophrenic a. (7-10th intercostal spaces) unnamed muscular branches intercostal muscles anteriorly; skin overlying the intercostal muscles there are two anterior intercostal aa. per side per intercostal space, one coursing above and one coursing below each rib
intercostal, highest costocervical trunk posterior intercostal aa. for intercostal spaces 1-2 intercostal muscles of intercostal spaces 1 and 2, vertebral column, deep back muscles highest intercostal a. is also known as: supreme intercostal a.
intercostal, posterior highest intercostal (upper 2 intercostal spaces), descending thoracic aorta (3rd-11th intercostal spaces) posterior br., spinal br., anterior br., collateral br., lateral cutaneous br. intercostal muscles, spinal cord and vertebral column, deep back muscles, skin and superficial fascia overlying the intercostal spaces posterior intercostal aa. supply the lateral and posterior portions of the intercostal space; anterior intercostal aa. supply the anterior portions of the intercostal spaces
musculophrenic internal thoracic a. anterior intercostal aa. anterior diaphragm, anterior aspects of intercostal spaces 7-10 or 11 musculophrenic a. supplies muscles that develop in the septum transversum
thoracic, internal subclavian a. (1st part) pericardiocophrenic a., perforating brs., anterior intercostal aa., mediastinal brs., thymic brs., musculophrenic a., superior epigastric a. mediastinum, anterior thoracic wall, anterior abdominal wall, respiratory diaphragm internal thoracic a. is also known as: internal mammary a.

Veins of the Thoracic Wall

VeinTributariesDrains IntoRegions DrainedNotes
intercostal, posterior lateral cutaneous br. 1st: brachiocephalic v.; 2nd-4th: superior intercostal v.; right 5th-11th: azygos v.; left 5th-7th or 8th: accessory hemiazygos v.; left 9th-11th: hemiazygos v. intercostal space including skin, muscles and adjacent ribs; the spinal cord at that segmental level and the corresponding vertebra the difference in termination of the intercostal vv. of the left and right sides is explained by the embryonic origin of the azygos system from the (originally symmetrical) supracardinal vv.
intercostal, superior 2nd-4th posterior intercostal vv. right: arch of the azygos v.; left: left brachiocephalic v, intercostal spaces 2-4 superior intercostal v. develops from the cephalic end of the supracardinal v. in the embryo


Fasciae of the Thorax

Structure Location/Description Notes
fascia, endothoracic connective tissue lining the inner aspect of the chest wall endothoracic fascia is located between the parietal pleura and the muscles and bones of the thoracic wall; it is equivalent to the transversalis fascia layer of the abdomen
fascia, Sibson's part of the scalene fascia that lines the cervical parietal pleura Sibson's fascia anchors the dome of cervical pleura; it is continuous with the endothoracic fascia at the level of the first rib

Joints of the Thoracic Wall

Joint or ligament Description Notes
costal cartilage the cartilage that caps the medial end of the rib costal cartilages of ribs 1-7 connect to the sternum; costal cartilages of ribs 8-10 connect to the costal cartilage of rib 7; costal cartilages of ribs 11 & 12 do not articulate anteriorly but end in the muscles of the abdominal wall
radiate sternocostal ligaments ligaments that reinforce the sternocostal joint capsule these ligaments connect the costal cartilages of ribs 1-7 with the sternum on both the anterior and posterior surfaces of the sternocostal articulation
sternal angle the angle formed by the articulation between the manubrium and the body of the sternum a synchondrosis; the cartilage within this joint usually does not become ossified until old age; the angle formed by this articulation is also called the angle of Louis; the sternal angle marks the level of the second costal cartilage from which all other ribs are counted
sternocostal joints the articulations that connect the costal cartilages with the sternum a synchondrosis (rib 1) or synovial joints (ribs 2-10); sternocostal synovial joints involving ribs 2-7 contain thin joint capsules; interchondral joints involving ribs 8-10 have simple gliding synovial articulations; radiate sternocostal ligaments reinforce the sternocostal articulations
xiphisternal joint the articulation that connects the xiphoid process with the body of the sternum a synchondrosis; the cartilage within this joint usually becomes ossified in old age; the xiphisternal joint marks the inferior extent of the thoracic cavity

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Some of the material presented in these tables is contained in the book:
MedCharts Anatomy by Thomas R. Gest and Jaye Schlesinger
Published by ILOC, Inc., New York. Copyright 1995.

Content of these tables has been edited for use in this course by Patrick W. Tank, Ph.D.
Copyright 2005, Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences.

Unauthorized use is prohibited.