bones of the thoracic wall

8/4/2019 Bones of the Thoracic Wall

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Bones of the Thoracic Wall

Bones of the Thoracic Wall

The osteocartilaginous thoracic cage is formed by part of the vertebral column(12 thoracic vertebrae and intervertebral discs); 12 pairs ofribs and costalcartilages, and the sternum. The ribs and the costal cartilages form the largest partof the thoracic cage.

The Thoracic Vertebrae (p. 33)

The special features of these vertebrae are: (1) they have facets on their bodiesfor articulation with the heads of ribs; (2) there are facets on their transverse

processes for articulation with the tubercles of ribs, except for the inferior two orthree ribs, and (3) they have long spinous processes.

The Costal Facets (p. 33)

Thoracic vertebrae are unique in that they have facets on their bodies and transverse

processes for articulation with ribs (T11 and T12 are exceptions).

Two demifacets are located laterally on bodies of T2 to T9. The superior demifacet

articulates with the head of its own rib and the inferior demifacet articulates with the

head of the rib inferior to it.

T1 has a single costal facet for the head of the firs rib and a small demifacet for the

cranial part of the second rib.

T10 has only one costal facet which is partly on its body and partly on its pedicle.

T11 and T12 have only a single costal facet on their pedicles.

The Spinous Processes (p. 33)

Spinous processes of T5 to T8 are nearly vertical and overlap the vertebrae like roof

shingles.

This arrangement covers the small intervals between the laminae of adjacent

vertebrae, thereby preventing sharp objects such as a knife from penetrating the

vertebral canal and injuring the spinal cord.

The spinous processes of T1, T2, T11 and T12 are horizontal, and those of T3, T4, T9

and T10 slope inferiorly

The Ribs (pp. 34-6)

There are usually 12 of these elongated flat bones on each side of the thorax.They form the largest part of the osteocartilaginous thoracic cage.


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The ribs curve anteriorly and inferiorly from the thoracic vertebrae.

Each typical rib has a head, neck, tubercle, and shaft.

The head of a rib is wedge-shaped and presents two articular facets for articulationwith the numerically corresponding vertebra and the vertebra superior to it.

These facets are separated by the crest of the head.

The neck of a rib is the stout, flattened part located between the head and thetubercle.

The neck lies anterior to the transverse process of the corresponding vertebra.

Its superior border, called the crest of the neck, is sharp, whereas its inferior borderis rounded.

The tubercle of a rib is on the posterior surface at the junction of its neck and shaftand is most prominent on the superior ribs.

The tubercles of most ribs have a smooth convex fact, which articulates with the

corresponding transverse process of the vertebra, and a rough non-articular part forattachment of the lateral costotransverse ligament.

The tubercles of the 8th

to 10th

ribs have flat facets for articulation with similar facets

on the transverse processes of the vertebrae.

The shaft (body) of a rib is thin, flat, and curved. Forming its largest part, theshaft has external and internal surfaces, thick and rounded superior borders, and thin,

sharp inferior borders.

A short distance beyond the tubercle, the shaft ceases to pass posteriorly and swings

sharply anteriorly.

The point of greatest curvature is the angle of the rib. Here the rib is both curvedand twisted.

The thorax of a person lying on his/her back is supported by the angle of the ribs and

the spinous processes of the vertebrae.

The costal groove (sulcus) and flange formed by the inferior border of the ribprotect the intercostal nerve and vessels that accompany the rib.

True Ribs (p. 35)

The first seven (and sometimes the eighth) pairs of ribs are called true orvertebrosternal ribs because they are connected to the sternum by theircostal cartilages.

False Ribs (p. 35)

The 8th

to 12th

pairs of ribs are false or vertebrochondral ribs. Each of the 8

thto 10

thribs is connected by its costal cartilage to the ribs superior to it.

The 11th and 12th pairs of false ribs are often called vertebral or floating ribsbecause they are unattached anteriorly.


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They end in the muscles of the anterior abdominal wall.

Atypical Ribs (pp. 35, 38)

The 1st, 2

nd, and 10

thto 12

thpairs of ribs are atypical.

The First Rib (pp 35, 38)

This is the broadest and most curved of all the ribs. It is also the shortest of thetrue ribs.

The first rib is clinically important because so many structures cross or attach to it.

It is flat and has a prominent scalene tubercle on the internal border of its superiorsurface for the attachment of the scalenus anterior muscle.

The subclavian vein crosses the first rib anterior to the scalene tubercle and thesubclavian artery.

The inferior trunk of the brachial plexus passes posterior to it. A distinct groove is formed by the subclavian vessels and brachial plexus on the

superior surface of the first rib.

This rib articulates with the body of the first thoracic vertebra. The prominent tubercle

of the first rib articulates with the transverse process of this vertebra.

The first rib is difficult to palpate due to the clavicle, but the first intercostal space can

be felt just inferior to the clavicle.

The Second Rib (p. 38)

This rib has a curvature similar to the first rib, but it is thinner, much less curved, and

is about twice as long as the first rib.

It can easily be distinguished from the first rib by the presence of a broad, rough

eminence, which is the tuberosity for the serratus anterior muscle.

The 10th Rib (p. 38)

This rib usually articulates with T10 vertebrae only.

The 11th and 12th Ribs (p. 38)

These ribs are short, especially the 12th

pair.

They are capped with a small costal cartilage, have a single facet on their heads, and

have no neck or tubercle. The 11

thrib has an ill-defined angle and a shallow costal groove.


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The 12th

rib has neither of these features and may be shorter than the first rib.

The Costal Cartilages (p. 39)

These hyaline cartilage bars are more rounded than the ribs, and extend from theanterior ends of the ribs.

The first seven, extend from the anterior ends of the ribs.

These seven pairs (and sometimes the eighth) are connected with the sternum.

The 8th

and 10th

pairs of costal cartilages articulate with the inferior border of the

cartilage of the preceding rib, and the costal cartilages of the 11th

and 12th

ribs are

pointed and end in the musculature of theanterior abdominal wall.

The costal cartilages contribute significantly to the elasticity and mobility of the ribs.

The Costal Margins (p. 39)

The medial ends of the seventh to tenth costal cartilages join to form a cartilaginous

costal margin on each side. Together, these margins form the costal arch. The angle formed where the right and left costal margins converge at the inferior end

of the body of the sternum is called the infrasternal angle. It is located at thexiphisternal joint, where the body of the sternum articulates with the xiphoidprocess.

Joints of the Ribs

Joints of the Ribs

The Costovertebral Joints

A typical rib articulates with the vertebral column at two joints: (1) the joints of the

heads of the ribs and (2) the costotransverse joints. Typically, the head of a rib articulates with the sides of the bodies of two thoracic

vertebrae, and the tubercle articulates with the tip of a transverse process.

The costovertebral joints are the plane type of synovial joint that allows forgliding or sliding motions.

Joints of the Head of the Ribs (p. 39)

The head of each typical rib articulates with the demifacets of two adjacent vertebrae

and the intervertebral disc between them.
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The head articulates with the superior part of the corresponding vertebra, the inferior

part of the vertebra superior to it, and the adjacent intervertebral disc.

The crest of the head is attached to the intervertebral disc by an intraarticularligament. It is located within the joint and divides it into two synovial cavities.

There are exceptions to this general arrangement. The 1st, sometimes the 10

th, and

usually the 11th

and 12th

ribs are connected only to their own vertebral bodies. In these

cases, there are no intraarticular ligaments and the joint cavities are not divided.

An articular capsule surrounds each joint and connects the head of the rib with thecircumference of the joint cavity.

The capsule is strongest anteriorly where a radiate ligament fans out from theanterior margin of the head of the rib to the sides of the bodies of two vertebrae and

the intervertebral disc between them.

The heads of the ribs are connected so closely to the vertebral bodies that only slight

gliding movements occur at the joints of the heads of the ribs.

The Costotransverse Joints (pp. 39-40)

The tubercle of a typical rib articulates with the facets on the tip of the transverse

process of its own vertebra to form a synovial joint. These small joints are surrounded by thin articular capsules, which are attached to the

edges of the articular facets.

A lateral costotransverse ligament, passing from the tubercle of the rib to thetip of the transverse process, strengthens the joint at each side.

In addition, a costotransverse ligament unties the posterior surface of the neck of the

rib to the anterior surface of the transverse process.

A superior costotransverse ligament joins the crest of the neck to thetransverse process superior to it.

The aperture between this ligament and the vertebral column permits passage of the

spinal nerve and the dorsal branch of the intercostal artery.

The 11th

and 12th

ribs do not articulate with transverse processes and have freer

movements as a result.

The strong costotransverse ligaments binding these joints limit their movements to

slight gliding. However, the tubercles of the superior six ribs are convex and fit into

concavities on the transverse processes.

As a result, some superior and inferior movements of the tubercles are associated with

rotation of the ribs.

The Sternocostal Joints (p. 40)


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The 1st

to 7th

ribs articulate via their costal cartilages with the lateral borders of the

sternum. The first pair of costal cartilages articulates with the sternum at primarycartilaginous joints (synchondroses).

The costal cartilages are united directly to the hyaline cartilage in the depressions

located art the superolateral margins of the manubrium of the sternum.

The 2nd

to 7th

pairs of costal cartilages articulates with the sternum at synovialjoints, but joint cavities are often absent in the inferior ones.

The thin, weak articular capsules of these joints are strengthened anteriorly and

posteriorly by radiate sternocostal ligaments. These thin, broad membranous bands pass from the costal cartilages to the anterior

and posterior surfaces of the sternum, forming a felt-like covering for the sternum.

The Costochondral Joints (p. 41)

Each rib has a cup-shaped depression on its anterior end into which its costal cartilage

fits.

The rib and its costal cartilage are firmly bound together by the continuity of the

periosteum of the rib with the perichondrium of the costal cartilages.

No movement normally occurs at these joints.

The Interchondral Joints (p. 41)

The articulations between the adjacent borders of the 6th and 7th, 7th and 8th, 8th and 9thcostal cartilages are plane synovial joints.

Each of these articulations is enclosed within an articular capsule that is lined with a

synovial membrane.

Interchondral ligaments strengthen the joints.

The articulation between the 9th

and 10th

costal cartilages is a fibrous joint.

The Sternum

The sternum (breastbone) is an elongated flat bone that resembles a shortbroadsword or dagger. It forms the middle part of the anterior wall of the thorax.

The sternum (G. sternon, chest) consists of three parts: manubrium, body andxiphoid process.

The Manubrium (p. 41)

The manubrium (L. handle), is the superior part of the sternum. It is located anterior

to T3 and T4 vertebrae.

It is wider and thicker than the other two parts of the sternum. Its narrow inferior endgives it a somewhat triangular shape


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Broad and thick superiorly, the manubrium slopes inferoanteriorly.

The superior surface of the manubrium is indented by the jugular notch(suprasternal notch), which can be easily palpated.

On each side of this notch there is an oval articular facet, called the clavicular

notch, which articulates with the medial end of the clavicle. Just inferior to the clavicular notch, the costal cartilage of the first rib is fused with the

lateral margin of the manubrium.

This is a flexible but strong primary cartilaginous joint.

The inferior border of the manubrium is oval and rough where it articulates with the

body of the sternum at the manubriosternal joint.

The manubrium and body lie in slightly different planes; hence, their junction forms a

projecting sternal angle (angle of Louis). The bony landmark is located opposite the second pair of costal cartilages.

The sternal angle is an important guide to the accurate numbering of theribs.

The Body of the Sternum (p. 41)

The body of the sternum is the longest of the three parts. It is located anterior to T5 to

T9 vertebrae.

It is longer, thinner, and narrower that the manubrium, but its width varies owing to

the scalloping of its lateral borders by the costal notches. The body is broadest at the level of the fifth pair of sternocostal joints and then

gradually tapers inferiorly.

The anterior surface of the body is slightly concave from side to side.

In young people four sternebrae are obvious. They articulate with each other atprimary cartilaginous joints.

The sternebrae begin to fuse from the inferior end between puberty and 25 years of

age.

In adults, the sternum is marked by three transverse ridges marking the lines of fusion

of the sternebrae may be visible in a sternum from a young adult, but they are less

distinct that the ridges on the anterior surface.

The Xiphoid Process (p. 41)

This is a thin sword-shaped process (G. xiphos, sword) is the smallest and most

variable part of the sternum. Although it is often pointed, the xiphoid process(xiphisternum) may be blunt, bifid, curved, or deflected to one side or anteriorly.

The xiphoid is cartilaginous at birth and remains so until early childhood. It maybegin to ossify during the third year of life and then it consists of a bony core

surrounded by hyaline cartilage. However, ossification usually does not begin untilmuch later.


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The xiphoid usually ossifies and unites with the body of the sternum around 40 years

of age, but it may not be united even in very old people.

The xiphoid process is an important landmark in the median plane for thefollowing reasons: (1) its junction with the body of the sternum at the xiphisternal

joint indicates the inferior limit of the thoracic cavity anteriorly and the site of theinfrasternal angle; and (2) it is a midline pointer to the diaphragmatic surface of the

liver, diaphragm, and inferior border of the hear.

Joints of the Sternum

Joints of the Sternum

The joints of the sternum are between its parts. There are two articulations: the manubriosternal (sternomanubrial) and xiphisternal

(xiphosternal) joints.

The Manubriosternal Joint (p. 43)

This articulation is between the manubrium and the body of the sternum.

The sternal angle indicates the manubriosternal joint. In adults this is asecondary cartilaginous joint (symphysis).

The bony articular surfaces are covered with hyaline cartilage, and afibrocartilaginous disc connects the articulation bones.

In about 30% of people, the central part of the cartilaginous disc undergoes

absorption, forming a cavity, but this is not a joint cavity. The manubriosternal joint is strengthened by anterior and posterior fibrous ligaments,

which extend across the joint from the manubrium to the body.

In most people, the manubriosternal joint moves slightly during respiration.

The Xiphisternal Joint (p. 44)

This articulation between the xiphoid process and body of the sternum is a primarycartilaginous joint (synchrondrosis); these bones are united by hyaline cartilage.

By 40 years of age, the xiphoid and this cartilage have usually ossified.

In most elderly people, the xiphisternal joint is ossified and the xiphoid is fused with

the body of the sternum.

The Intercostal Area


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The Intercostal Muscles

The External Intercostal Muscles (p. 50)

Each of the 11 pairs of muscles occupy the intercostal spaces from the tubercles ofthe ribs posteriorly to the costochondral junctions anteriorly.

Anteriorly, the external intercostal membranes replace the muscle fibres.

The muscles run inferoanteriorly from the rib above to the rib below.

Each muscle is attached superiorly to the inferior border of the rib and inferiorly to

the superior border of the rib below.

The external intercostal muscles are continuous inferiorly with theexternaloblique musclesof the anterolateral abdominal wall.

The Internal Intercostal Muscles (pp. 50-1)

The 11 pairs of muscles run deep to and at right angles to the external intercostalmuscles.

Their fibres run inferoposteriorly from the floors of the costal grooves to the superior

borders of the ribs inferior to them.

The internal intercostal muscles attach to the shafts of the ribs and their costal

cartilages as far anteriorly as the sternum and as far posteriorly as the angles of theribs.

Between the ribs posteriorly, the internal intercostal membrane replaces the internal

intercostal muscles.

The inferior internal intercostal muscles are continuous with theinternal obliquemusclesof the anterolateral abdominal wall.

The Innermost Intercostal Muscles (p. 51)

Theses are the deepest intercostal muscles and are similar to the internal intercostalmuscles, and are really deep portions of them.

The innermost intercostal muscles are separated from the internal intercostal muscles

by the intercostal nerves and vessels.

These muscles pass between the internal surfaces of adjacent ribs and occupy the

middle part of the intercostal spaces.

The Subcostal Muscles (p. 51)

These are variable in size and shape, these muscles are thin muscular slips that
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extend from the internal surface of the angle of the rib to the internal surface of the

rib inferior to it.

It crosses one or two intercostal spaces.

They run in the same direction as the internal intercostal muscles and lie internal to

them.

The Transversus Thoracic Muscle (p. 51)

These are thin muscular consisting of four or five slips that are attached posteriorly to

the xiphoid process, the inferior part of the body of the sternum, and the adjacent

costal cartilages.

They pass superolaterally and are attached to the second to sixth costal cartilages.

The transversus thoracis muscles are continuous inferiorly with thetransversusabdominis muscle. The internal thoracic vessels run anteriorly to these muscles,

between them and the costal cartilages and internal intercostal muscles.

Actions of the Intercostal Muscles (p. 51)

All these inspiratory muscles elevate the ribs. This movement expands the thoracic cavity in the transverse and anteroposterior

diameters.

All three layers of intercostal muscles keep the intercostal spaces rigid,

thereby preventing them from bulging out during expiration and from being drawn induring inspiration.

The Intercostal Spaces

These spaces between the ribs are deeper anteriorly than posteriorly and deeper

between the superior than the inferior ribs.

The intercostal spaces widen on inspiration. Each space contains three muscles and a neurovascular bundle (vein, artery and

nerve; often referred to as VAN).

Intercostal Nerves (Moore p. 52, Snell 52-3)

There are 12 pairs of costal nerves. The intercostal nerves are the anterior rami of the first 11 thoracic spinal

nerves. The anterior ramus of the twelfth thoracic nerve lies in the abdomen andruns forward in the abdominal wall as the subcostal nerve.

Each intercostal nerve enters the intercostal space between the parietal pleura and the

posterior intercostal membrane.
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It then runs forward, inferior to the intercostal vessels in the costal groove of the

corresponding rib, between transversus thoracis and internal intercostal muscle.

The first 6 nerves are distributed within their intercostal spaces.

The seventh to ninth intercostal nerves leave the anterior ends of their intercostal

spaces by passing deep to the costal cartilages, to enter the anterior abdominal wall. In the case of the tenth and eleventh nerves, since the corresponding ribs are floating,

these nerves pass directly into the abdominal wall.

The lower intercostal nerves supply the skin of the abdomen. Also, these nerves also

supply the muscles of the abdomen-leading to the tickle response.

Branches of the intercostal nerves (Moore p. 56, Snell p. 53)

Rami communicantes connect the intercostal nerve to a ganglion of thesympathetic trunk. The grey ramus joins the nerve medial to the point at which the

white ramus leaves it.

A collateral branch, which runs forward inferiorly to the main nerve on the upperborder of the rib below.

A lateral cutaneous branch, which reaches the skin near the midaxillary line. Itdivides into an anterior and a posterior branch.

An anterior cutaneous branch, which is the terminal portion of the main trunk,reaches the skin near the midline. It divides into a medial and a lateral branch.

The main nerve and its collateral branch give off numerous muscular branches.

The first intercostal nerve has no anterior cutaneous branch and usuallyhas no lateral cutaneous branch. It divides into a large superior part and a small inferior part.

The superior part joins the brachial plexus. The inferior part becomes thefirst intercostal nerve

The second intercostal nerve may also contribute a small branch to the brachialplexus.

The lateral cutaneous branch of the second intercostal nerve is called the

intercostobrachial nerve because it supplies the floor of the axilla and thencommunicates with the medial brachial cutaneous nerve to supply the medial side of

the upper limb as far as the elbow.

The Intercostal Arteries

Three arteries, a large posterior intercostal artery and a small pair of anterior

intercostal arteries supply each intercostal space.

The Posterior Intercostal Arteries (p. 59)

The first two posterior intercostal arteries arise from the superior intercostal


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artery, a branch of the costocervical trunk of the subclavian artery. Nine pairs of posterior intercostal arteries and one pair of subcostal arteries arise

posteriorly from the thoracic aorta.

Each posterior intercostal artery gives off a posterior branch, which accompanies

the dorsal ramus of the spinal nerve to supply the spinal cord, vertebral column, backmuscles, and skin.

Each artery also gives off a small collateral branch that crosses the intercostalspace and runs along the superior border of the rib inferior to the space.

The terminal branches of the posterior intercostal artery anastomose anteriorly with

the anterior intercostal artery.

The posterior intercostal artery accompanies the intercostal nerve through the

intercostal space.

Close to the angle of the rib, it enters the costal groove, where it lies between the

intercostal vein and nerve. At first, the artery runs between the pleura and the internal

intercostal membrane and then it runs between the innermost intercostal andinternal intercostal muscles.

The Anterior Intercostal Arteries (p. 59)

The anterior intercostal arteries supplying the superior six intercostal spacesare derived from the internal thoracic arteries.

There are two anterior intercostal arteries for each intercostal space. The arteries

supplying the seventh to ninth intercostal spaces are derived from themusculophrenic arteries, branches of the internal thoracic arteries.

These arteries pass laterally, one near the inferior margin of the superior rib and the

other near the superior margin or the inferior rib.

At their origins, the first two arteries lie between the pleura and the internalintercostal arteries.

The next four arteries are separated from the pleura by the transversus thoracis

muscle.

The anterior intercostal arteries supply the intercostal muscles, and send branches

through them to the pectoral muscles, breast and skin.

There are no anterior intercostal arteries in the inferior two intercostalspaces. The posterior intercostal arteries and their collateral branches supply thesespaces.

The Intercostal Veins (p. 59)

The intercostal veins accompany the intercostal arteries and nerves; they lie deepest

in the costal grooves.

There are eleven posterior intercostal veins and one subcostal vein on eachside.


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They receive lateral cutaneous, muscular, intervertebral, and posterior tributaries.

The intercostal veins contain valves, which direct the blood posteriorly. The posterior intercostal veins anastomose with the anterior intercostal veins,

which are tributaries of the internal thoracic veins.

Most intercostal veins end in the azygos vein which conveys blood to thesuperior vena cava.

The superior intercostal veins drain directly into the superior vena cava.

The Internal Thoracic Vessels

The Internal Thoracic Artery (p. 59)

This vessel arises in the root of the neck from the inferior surface of the first part ofthe subclavian artery at the medial border of the scalenus anterior muscle.

The internal thoracic artery descends into the thorax posterior to the clavicle and the

first costal cartilage. It runs on the internal surface of the thorax, a little lateral to the

sternum.

It lies on the pleura posteriorly and is crossed by the phrenic nerve. The internal thoracic artery runs inferiorly in the thorax posterior to the superior six

costal cartilages and intervening intercostal muscles.

At the level of the third costal cartilage, it continues inferiorly, anterior to the

transverse thoracis muscle, to end in the sixth intercostal space where itdivides into the superior epigastric and musculophrenic arteries.

The Internal Thoracic Veins (pp. 59-60)

These are the venae comitantes of the internal thoracic artery. In the region of the first to third intercostal space, the usually unite to form a trunk

(single vein) that empties into the corresponding brachiocephalic vein; however,the right internal thoracic trunk may empty into the superior vena cava.

The Thoracic Diaphragm

The Thoracic Diaphragm

The thoracic diaphragm is a dome-shaped musculotendinous partition between the

thoracic and abdominal cavities.

The convexity of its dome bulges into the thoracic cavity during expiration.

The diaphragm is the principal muscle of respiration and forms the floor of thethoracic cavity and the roof of the abdominal cavity.

During respiration, it descends as it contracts and ascends as it relaxes.


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Structure of the Thoracic Diaphragm (pp. 224-7)

The diaphragm is composed of two portions: a peripheral muscular part, and a

central aponeurotic part, the central tendon.

The Muscular Part of the Diaphragm (pp. 224-5)

The fibres forming this part converge radially to the central tendon. Because theyhave distinct attachments, the muscular part is descriptively divided in the sternal,costal, and lumbar parts.

The Sternal Part (p. 224)

This portion consists of two small muscular slips that are attached to the posterioraspect of the xiphoid process. These slips converge radially to the centraltendon.

On each side of these muscular slips, there is a small anterolateral gap known as the

sternocostal hiatus.

The Costal Part (pp. 224-5)

This portion consists of wide muscular slips that arise from the internal surfaces of

the inferior six ribs and their costal cartilages on each side.

These slips interdigitate with slips of the transversus abdominis muscles.

The costal part forms the left and right hemidiaphragms or domes that move during

respiration.

The Lumbar Part (p. 225)

This portion arises from the lumbar vertebrae by two musculotendinous crura(L. legs), which are attached on each side of the aorta to the anterolateralsurfaces of the superior two (left) or three (right) lumbar vertebrae andtheir intervertebral discs.

The crura of the diaphragm blend with the anterior longitudinal ligament of thevertebral column.

The right crus is broader and longer than the left crus.

The crura are united opposite the disc between T12 and L1 vertebrae by a tendinousband or narrow arch called the median arcuate ligament


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It passes over the anterior surface of the aorta and provides attachment for some

fibres of the right crus.

The medial arcuate ligaments are thickenings of the anterior layer of thethoracolumbar fascia over the superior parts of thepsoas major muscles.

Each ligament forms a fibrous arch that runs from the crus of the diaphragm, anteriorto the psoas major muscle, and attaches to the transverse process of L1 vertebra.

The lateral arcuate ligaments are thickenings of the anterior layer of thethoracolumbar fascia over the superior parts of thequadratus lumborummuscles.

Each ligament forms a fibrous arch that runs from the transverse process of L1to the 12th rib.

The Central Part of the Diaphragm (pp. 225, 227)

The muscular fibres of the diaphragm converge radially to a strong, sheet-like

aponeurosis called the central tendon, which is fused with the inferior surface ofthe fibrous pericardium.

The central tendon has no bony attachments and is incompletely divided into three

leaves, which resemble a cloverleaf. This gives it a C-shape.

The right lateral leaf is the largest; the anterior (middle) leaf is intermediate in size,

and the left one is the smallest.

The lateral leaves curve posteriorly as they blend with the corresponding halves of

the diaphragm.

The anterior leaf lies just inferior to the heart.

The Diaphragmatic Apertures

There are several apertures in the diaphragm that permits structures to pass between

the thorax and abdomen. The major orifices are the venal caval foramen, the

oesophageal hiatus, and the aortic hiatus.

The Vena Caval Foramen (p. 227)

The foramen for the inferior vena cava is at the posterior junction of the right and

anterior leaves of the central tendon.

It is located at the level ofT8 vertebra, 2 to 3 cm to the right of the medial plane. It is the most superior of the three large apertures of the diaphragm.

The inferior vena cava is adherent to the margin of the vena caval foramen;

consequently, when the diaphragm contracts during inspiration, it widens the

foramen and stretches and dilates the inferior vena cava.
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These changes facilitate the blood flow through the inferior vena cava.

The Oesophageal Hiatus (p. 227)

The oesophagus passes obliquely through this oval aperture in the muscular part of

the diaphragm, posterior and to the left of the vena caval foramen.

The hiatus is usually in the right crus of the diaphragm, 2 to 3 cm left of the medial

plane and approximately at the level ofT10 vertebra.

The fleshy fibres of the right crus form the oesophageal sphincter, which constricts

the distal end of the oesophagus during inspiration, helping to prevent reflux of

gastric contents into the oesophagus.

The Aortic Hiatus (p. 277)

The aorta does not pierce the diaphragm because this aperture is posterior to it.

It passes posterior to the median arcuate ligament, which arches between the crura,

anterior to T12 vertebra and to the left of the median plane. The aorta is unaffected by the contraction of the diaphragm because it does not pass

through it.

The aortic hiatus also transmits the thoracic duct and the azygos vein.

Vessels and Nerves of the Diaphragm

Arterial Supply of the Diaphragm (p. 227)

Superior surface: superior phrenic arteries (arise from the thoracic aorta), andthe musculophrenic and pericardiophrenic arteries (branches of the internalthoracic).

Inferior surface: inferior phrenic arteries (branches of the abdominal aorta).

Venous Drainage of the Diaphragm (pp. 227-8)

Superior surface: pericardiophrenic and musculophrenic veins, which draininto the internal thoracic vein.

Inferior surface: inferior phrenic veins. The right inferior phrenic vein usually opens into the inferior vena cava, whereas the

left inferior phrenic vein usually joins the left suprarenal vein.

Innervation of the Diaphragm (p. 228)


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The entire motor supply to the diaphragm is from thephrenic nerves, which arise

from the ventral rami of segments C3-5 of the spinal cord. The phrenic nerves also supply sensory fibres to most of the diaphragm.

Peripheral parts of the diaphragm receive their sensory supply from the inferior six or

seven intercostal nerves and subcostal nerve.

Actions of the Diaphragm (p. 228)

The diaphragm is the chief muscle of inspiration. When it contracts its right and left domes move inferiorly so that its convexity is

flattened. The descent of the domes increases the vertical diameter of the thoracic

cavity.

As the diaphragm descends, the intra-thoracic pressure is decreased and the intra-

abdominal pressure is increased.

Diaphragmatic movements are also important in blood circulation because ofthe changes in pressure in the thoracic and abdominal cavities accompanying the

contraction of the diaphragm. Blood from the inferior vena cava is forced superiorly

into the heart.

The diaphragm is also an important muscle for abdominal straining. It assists theanterior abdominal muscles in raising intra-abdominal pressure during micturition

(urination), defecation (bowel movements), and parturition (childbirth).

The Mammary Glands

The Mammary Glands

Both men and women have breasts; normally they are well developed only in women.

They are situated on the anterior surface of the thorax, overlying the pectoralmuscles(pectoralis majorandserratus anterior).

The mammary glands are accessory organs of the female reproductive system. They

secrete milk for the nourishment of the infant in a process called lactation. They often extend toward the axillae forming axillary tails.

The amount of fat surrounding the glandular tissue determines the size of the breasts.

The Female Breasts

The lactiferous ducts give rise to buds that form 15 to 20 lobules of glandular tissue,

which constitute the mammary gland. Each lobule is drained by a lactiferous duct, which opens on the nipple. These ducts extend from the nipple in a manner similar to spokes of a wheel.

Deep to the areola, each duct has a dilated portion called the lactiferous sinus, inwhich milk accumulates during lactation.
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The Areolae (p. 45)

These contain numerous sebaceous glands, which enlarge during pregnancy and

secrete an oily substance that provides a protective lubricant for the areola and nipple. The areolae are variable in size, and are pink in white nulliparous women (who

have not borne children). During the first pregnancy, the areolae of white women

change permanently to brown.

There is now fat beneath the areolae.

The Nipples (p. 45)

There are conical or cylindrical prominences that are located in the centre of the

areolae. There is no fat in the nipples. In nulliparous women they are usually located at the level of the fourth intercostal

space. However, the position of the nipple varies considerable and cannot be used asa guide to the fourth intercostal spaces.

The tip of the nipple is fissured and contains the openings of the lactiferous ducts.

The nipples are composed mostly of circularly arranged smooth muscle that

compresses the lactiferous ducts and erects the nipples when they contract.

Description (p. 46)

The mammary gland is a modified sweat glandthis explains why it has nospecial capsule or sheath.

It lies in the superficial fascia, anterior to the thorax. The deep aspect of the breast is separated from the pectoral muscles by the deep

fascia.

Between the breast and the deep fascia, there is an area of loose connective tissue that

contains little fat.

This zone is called the retromammary space (bursa), and allows the breast to

move freely on the deep fascia covering the pectoralis major muscle.

Although it is easily separated from the deep fascia, the mammary gland if firmly

bound to the skin of the breast by suspensory ligaments(Coopers ligaments). These fibrous band which supports the breast, runs between the skin and deep fascia.

The rounded contour and most of the bulk of the breasts are produced by fat lobules.

The shape of the breast varies considerably in different persons and races and in the

same person at different ages.

Although breasts vary in size, their roughly circular bases are fairly constant and have

the following limits in well-developed females: vertically from the second to


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sixth ribs and laterally from the edge of the sternum to the midaxillaryline.

Two-thirds of the breast rest on the pectoralis major muscle; one-third covers the

serratus anterior muscle.

Its inferior border overlaps the superior part of the rectus sheath.

The Pectoralis Major Muscle (p. 507)

This large, thick, fan-shaped muscle covers the superior part of the thorax.

Its lateral border forms the anterior axillary fold and most of the anterior wall ofthe axilla.

The fascial sheath enclosing the pectoralis major muscle is attached at its origin to the

clavicle and sternum.

It leaves the lateral border of this muscle to form the axillary fascia in the floor ofthe axilla.

The pectoralis major and the deltoid muscles diverge slightly from each other

superiorly and, and along with the clavicle, form the deltopectoral triangle(infraclavicular fossa).

Thecephalic vein, one of the two major superficial veins of the upper limb, occupies

the furrow between the deltoid and pectoris major muscles before it enters the

deltopectoral triangle.

Proximal attachments are: clavicular head-anterior surface of the medial half ofclavicle;

sternocostal head-anterior surface of sternum, superior six costal

cartilages, and aponeurosis of the external oblique muscle.

Distal attachments are: lateral lip of intertubercular groove of humerus.

Innervation: lateral and medial pectoral nerves; clavicular head (C5 and C6),

sternoclavicular head (C7, C8, and T1)

When both parts of the muscle act together, the pectoralis major adducts and medially

rotates the humerus at the shoulder joint.

Acting alone, the clavicular head helps to flex the humerus and from thisposition the sternocostal head extends the humerus. When the arm is flexed,the sternocostal head raises the ribs during forced inspiration.

The Pectoralis Minor Muscle (p. 507)

This triangular muscle lies in the anterior wall of the axilla, where it is largely covered

by the much larger pectoralis major.

The pectoralis minor is the landmark of the axilla. Along with the coracoid process of the scapula, it forms an arch deep to which pass

the vessels and nerves to the upper limb.

The pectoralis minor is surrounded by clavipectoral fascia, a thin sheet of fibroustissue that runs from the clavicle superiorly to the axillary fascia inferiorly.
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Proximal attachments are: ribs 3 to 5 near their costal cartilages.

Distal attachments are: medial border and superior surface of coracoid process of

scapula.

Innervation: medial pectoral nerve (C8 and T1)

The Serratus Anterior Muscle (pp. 507, 510)

This is a large, foliate muscle that overlies the lateral portion of the thorax and the

intercostal muscles.

It was given its name (L. serratus, a saw) because the saw-toothed appearance of the

fleshy digitations at its proximal attachments.

Proximal attachments are: external surface of lateral parts of ribs 1 to 8.

Distal attachments are: anterior surface of medial border of scapula.

Innervation: long thoracic nerve (C5, C6, and C7).

The serratus anterior protracts the scapula and holds or fixes it against the thoracicwall.

Because it is active during punching, it has been called "the boxer's muscle".

By fixing the scapula to the thorax, it acts as an anchor for this bone and permits other

muscles to use it as a fixed bone to produce movements of the humerus. Inferior fibres

of the serratus anterior help to raise the glenoid fossa of the scapula.

Injuries involving the Serratus Anterior Muscle

When a person's serratus anterior muscle is paralysed owing to injury to the longthoracic nerve, the medial border of the scapula stands out, especially its inferiorangle, giving it the appearance of a wing when the person presses anteriorly.

Consequently this condition is called a "wing scapula". When the arm is raised, the

scapula is pulled away from the thoracic wall.

In addition the arm cannot be abducted farther than the horizontal position because

the serratus anterior is unable to rotate the scapula and raise the glenoid fossa.

Arterial Supply of the Breast (p. 46)

There is abundant blood supply to the breast.

The arteries are mainly from the internal thoracic artery via its perforating

branches, which pierce the 2nd

to 4th

intercostal spaces. The breast also receives several branches from the axillary artery, mainly from its

lateral thoracic and thoracoacromial branches, and lateral and anteriorbranches from the intercostal arteries (in the 3rd to 5th intercostal spaces).

Venous Drainage of the Breast (p. 46)

Veins from the breast drain into the axillary, internal thoracic, lateral thoracic and

intercostal veins.

The chief venous drainage is the axillary vein.


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Lymphatic Drainage of the Breast (p. 46)

Most of the lymphatic drainage (about 75%) is to the axillary lymph nodes,

mainly the pectoral group. Lymph from the medial part of the breast drains into the parasternal lymph

nodes, which are located within the thorax along the internal thoracic vessels.

bones of the thoracic wall

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