T O R A X D R A K E

Conceptual overview 124 Diaphragm 156
Venous drainage 160
General description 124 Innervation 160
Functions 125 Movements of the thoracic wall and
Breathing 125 diaphragm during breathing 160
Protection of vital organs 125 Pleural cavities 160
Conduit 125 Pleura 160
Component parts 125 Lungs 165
Thoracic wall 125 Mediastinum 178
Superior thoracic aperture 126 Middle mediastinum 178
Inferior thoracic aperture 126 Superior mediastinum 206
Diaphragm 127 Posterior mediastinum 217
Mediastinum 127 Anterior mediastinum 225
Pleural cavities 127
Relationship to other regions 130
Neck 130 Surface anatomy 226
Upper limb 130
Abdomen 131 Thorax surface anatomy 226
Breast 131 How to count ribs 226
Key features 132 Surface anatomy of the breast in women 227
Vertebral level TIV/V 132 Visualizing structures at the TIV/V
Venous shunts from left to right 132 vertebral level 228
Segmental neurovascular supply of Visualizing structures in the superior
thoracic wall 132 mediastinum 228
Sympathetic system 135 Visualizing the margins of the heart 228
Flexible wall and inferior thoracic aperture 135 Where to listen for heart sounds 229
Innervation of the diaphragm 137 Visualizing the pleural cavities and lungs,
pleural recesses, and lung lobes and
fissures 229
Regional anatomy 139 Where to listen for lung sounds 230

Pectoral region 139
Breast 139 Clinical cases 235
Venous drainage 139
Muscles of the pectoral region 141
Thoracic wall 142
Skeletal framework 142
Intercostal spaces 149

Drake_ch03_main.indd 2 8/25/2008 4:10:06 PM

3
Thorax


Thorax

Conceptual overview
GENERAL DESCRIPTION
The thorax is an irregularly shaped cylinder with a narrow The musculoskeletal wall of the thorax is flexible and
opening (superior thoracic aperture) superiorly and a rela consists of segmentally arranged vertebrae, ribs, muscles,
tively large opening (inferior thoracic aperture) inferiorly and the sternum.
(Fig. 3.1). The superior thoracic aperture is open, allowing The thoracic cavity enclosed by the thoracic wall
continuity with the neck; the inferior thoracic aperture is and the diaphragm is subdivided into three major
closed by the diaphragm. compartments:

Superior thoracic aperture
Vertebral column

Mediastinum

Right pleural cavity Left pleural cavity
Rib I

Manubrium of sternum

Sternal angle

Body of sternum

Ribs

Xiphoid process
Diaphragm

Inferior thoracic aperture

Fig. 3.1 Thoracic wall and cavity.
3-


Conceptual overview • component parts 3
■ a left and a right pleural cavity, each surrounding a The esophagus, vagus nerves, and thoracic duct pass
lung; through the mediastinum as they course between the
■ the mediastinum. abdomen and neck.
The phrenic nerves, which originate in the neck, also
The mediastinum is a thick, flexible soft tissue partition pass through the mediastinum to penetrate and supply the
oriented longitudinally in a median sagittal position. It diaphragm.
contains the heart, esophagus, trachea, major nerves, and Other structures such as the trachea, thoracic aorta,
major systemic blood vessels. and superior vena cava course within the mediastinum en
The pleural cavities are completely separated from each route to and from major visceral organs in the thorax.
other by the mediastinum. Therefore, abnormal events in
one pleural cavity do not necessarily affect the other cavity.
This also means that the mediastinum can be entered sur COMPONENT PARTS
gically without opening the pleural cavities.
Another important feature of the pleural cavities is that Thoracic wall
they extend above the level of rib I. The apex of each lung The thoracic wall consists of skeletal elements and
actually extends into the root of the neck. As a conse muscles (Fig. 3.1):
quence, abnormal events in the root of the neck can involve
the adjacent pleura and lung, and events in the adjacent ■ posteriorly, it is made up of twelve thoracic vertebrae
pleura and lung can involve the root of the neck. and their intervening intervertebral discs;
■ laterally, the wall is formed by ribs (twelve on each
side) and three layers of flat muscles, which span the
FUNCTIONS intercostal spaces between adjacent ribs, move the ribs
and provide support for the intercostal spaces;
Breathing ■ anteriorly, the wall is made up of the sternum, which
One of the most important functions of the thorax is breath consists of the manubrium of sternum, body of sternum,
ing. The thorax not only contains the lungs but also pro and xiphoid process.
vides the machinery necessary—the diaphragm, thoracic
wall, and the ribs—for effectively moving air into and out The manubrium of sternum, angled posteriorly on the
of the lungs. body of sternum at the manubriosternal joint, forms the
Up and down movements of the diaphragm and changes sternal angle, which is a major surface landmark used
in the lateral and anterior dimensions of the thoracic wall, by clinicians in performing physical examinations of the
caused by movements of the ribs, alter the volume of the thorax.
thoracic cavity and are key elements in breathing. The anterior (distal) end of each rib is composed of costal
cartilage, which contributes to the mobility and elasticity
of the wall.
Protection of vital organs All ribs articulate with thoracic vertebrae posteriorly.
The thorax houses and protects the heart, lungs, and Most ribs (from rib II to IX) have three articulations
great vessels. Because of the domed shape of the diaphragm, with the vertebral column. The head of each rib articulates
the thoracic wall also offers protection to some important with the body of its own vertebra and with the body of the
abdominal viscera. vertebra above (Fig. 3.2). As these ribs curve posteriorly,
Much of the liver lies under the right dome of the dia each also articulates with the transverse process of its
phragm, and the stomach and spleen lie under the left. The vertebra.
posterior aspects of the superior poles of the kidneys lie on Anteriorly, the costal cartilages of ribs I to VII articulate
the diaphragm and are anterior to rib XII, on the right, and with the sternum.
to ribs XI and XII, on the left. The costal cartilages of ribs VIII to X articulate with the
inferior margins of the costal cartilages above them. Ribs
XI and XII are called floating ribs because they do not
Conduit articulate with other ribs, costal cartilages, or the sternum.
The mediastinum acts as a conduit for structures that pass Their costal cartilages are small, only covering their tips.
completely through the thorax from one body region to The skeletal framework of the thoracic wall provides
another and for structures that connect organs in the extensive attachment sites for muscles of the neck,
thorax to other body regions. abdomen, back, and upper limbs. 3-


Thorax

Superior articular process Superior costal facet

Costal facet of
transverse process

Sternum
Inferior articular Intervertebral disc
process
Vertebral body

Inferior costal facet
Rib V

Costal cartilage

Fig. 3.2 Joints between ribs and vertebrae.

A number of these muscles attach to ribs and function between the neck and head and the thorax pass more verti
as accessory respiratory muscles; some of them also stabi cally through the superior thoracic aperture.
lize the position of the first and last ribs.

Inferior thoracic aperture
The inferior thoracic aperture is large and expand
Superior thoracic aperture able. Bone, cartilage, and ligaments form its margin
Completely surrounded by skeletal elements, the superior (Fig. 3.4A).
thoracic aperture consists of the body of vertebra TI pos The inferior thoracic aperture is closed by the dia
teriorly, the medial margin of rib I on each side, and the phragm, and structures passing between the abdomen and
manubrium anteriorly. thorax pierce or pass posteriorly to the diaphragm.
The superior margin of the manubrium is in approxi Skeletal elements of the inferior thoracic aperture are:
mately the same horizontal plane as the intervertebral disc
between vertebrae TII and TIII. ■ the body of vertebra TXII posteriorly;
The first ribs slope inferiorly from their posterior articu ■ rib XII and the distal end of rib XI posterolaterally;
lation with vertebra TI to their anterior attachment to the ■ the distal cartilaginous ends of ribs VII to X, which unite
manubrium. Consequently, the plane of the superior tho to form the costal margin anterolaterally; and
racic aperture is at an oblique angle, facing somewhat ■ the xiphoid process anteriorly.
anteriorly.
At the superior thoracic aperture, the superior aspects The joint between the costal margin and sternum lies
of the pleural cavities, which surround the lungs, lie on roughly in the same horizontal plane as the intervertebral
either side of the entrance to the mediastinum (Fig. disc between vertebrae TIX and TX. In other words, the post
3.3). erior margin of the inferior thoracic aperture is inferior to
Structures that pass between the upper limb and thorax the anterior margin.
3- pass over rib I and the superior part of the pleural cavity as When viewed anteriorly, the inferior thoracic aperture
they enter and leave the mediastinum. Structures that pass is tilted superiorly.


Conceptual overview • component parts 3
Esophagus
Common carotid artery

Vertebra TI

Trachea
Superior thoracic aperture

Rib I Internal
jugular vein

Apex of right lung

Subclavian
artery and vein Manubrium
of sternum

Rib II

Fig. 3.3 Superior thoracic aperture.

A B

Right dome

Central
tendon
Xiphoid process

Inferior thoracic Left dome
aperture
Distal cartilaginous
ends of ribs VII to X;
costal margins
Esophageal
hiatus
Rib XI
Rib XII Aortic
hiatus
Vertebra TXII

Fig. 3.4 A. Inferior thoracic aperture. B. Diaphragm.

Diaphragm Because of the oblique angle of the inferior thoracic
The musculotendinous diaphragm seals the inferior tho aperture, the posterior attachment of the diaphragm is
racic aperture (Fig. 3.4B). inferior to the anterior attachment.
Generally, muscle fibers of the diaphragm arise radially, The diaphragm is not flat; rather, it “balloons” superi
from the margins of the inferior thoracic aperture, and orly, on both the right and left sides, to form domes. The 3-
converge into a large central tendon. right dome is higher than the left, reaching as far as rib V.


Thorax

As the diaphragm contracts, the height of the domes Each pleural cavity is completely lined by a mesothe
decreases and the volume of the thorax increases. lial membrane called the pleura.
The esophagus and inferior vena cava penetrate the dia During development, the lungs grow out of the medias
phragm; the aorta passes posterior to the diaphragm. tinum, becoming surrounded by the pleural cavities. As
a result, the outer surface of each organ is covered by
pleura.
Mediastinum Each lung remains attached to the mediastinum by a
The mediastinum is a thick midline partition that extends root formed by the airway, pulmonary blood vessels, lym
from the sternum anteriorly to the thoracic vertebrae phatic tissues, and nerves.
posteriorly, and from the superior thoracic aperture to the The pleura lining the walls of the cavity is the parietal
inferior thoracic aperture. pleura, whereas that reflected from the mediastinum at the
A horizontal plane passing through the sternal angle roots and onto the surfaces of the lungs is the visceral
and the intervertebral disc between vertebrae TIV and pleura. Only a potential space normally exists between the
TV separates the mediastinum into superior and inferior visceral pleura covering lung and the parietal pleura lining
parts (Fig. 3.5). The inferior part is further subdivided by the wall of the thoracic cavity.
the pericardium, which encloses the pericardial cavity sur The lung does not completely fill the potential space
rounding the heart. The pericardium and heart constitute of the pleural cavity, resulting in recesses, which do not
the middle mediastinum. contain lung and are important for accommodating
The anterior mediastinum lies between the sternum changes in lung volume during breathing. The costodia
and the pericardium; the posterior mediastinum lies be phragmatic recess, which is the largest and clinically most
tween the pericardium and thoracic vertebrae. important recess, lies inferiorly between the thoracic wall
and diaphragm.

Pleural cavities
The two pleural cavities are situated on either side of the
mediastinum (Fig. 3.6).

Sternal angle Rib I
I

Superior mediastinum
IV

V
Anterior mediastinum

Middle mediastinum

Posterior mediastinum
Inferior mediastinum
X

Diaphragm
XII

Fig. 3.5 Subdivisions of the mediastinum.
3-


Conceptual overview • Relationship to other regions 3
Apex of right lung Trachea

Left pleural cavity

Right main bronchus

Parietal pleura

Visceral pleura
Mediastinum

Costodiaphragmatic
recess
Diaphragm

Superior thoracic aperture Rib I
Fig. 3.6 Pleural cavities.
Esophagus Scapula

Brachial plexus Axillary inlet

RELATIONSHIP TO
OTHER REGIONS
Neck
The superior thoracic aperture opens directly into the root
of the neck (Fig. 3.7).
The superior aspect of each pleural cavity extends
approximately 2–3 cm above rib I and the costal cartilage
into the neck. Between these pleural extensions, major
visceral structures pass between the neck and superior
mediastinum. In the midline, the trachea lies immediately Subclavian Trachea Coracoid
artery and vein process
anterior to the esophagus. Major blood vessels and nerves Clavicle
pass in and out of the thorax at the superior thoracic aper
Fig. 3.7 Superior thoracic aperture and axillary inlet.
ture anteriorly and laterally to these structures. 3-


Thorax

num to supply anterior aspects of the thoracic wall. Those
Upper limb branches associated mainly with the second to fourth
An axillary inlet, or gateway to the upper limb, lies on intercostal spaces also supply the anteromedial parts of
each side of the superior thoracic aperture. These two axil each breast.
lary inlets and the superior thoracic aperture communi Lymphatic vessels from the medial part of the breast
cate superiorly with the root of the neck (Fig. 3.7). accompany the perforating arteries and drain into the
Each axillary inlet is formed by: parasternal nodes on the deep surface of the thoracic
wall:
■ the superior margin of the scapula posteriorly;
■ the clavicle anteriorly; and ■ vessels and lymphatics associated with lateral parts
■ the lateral margin of rib I medially. of the breast emerge from or drain into the axillary
region of the upper limb;
The apex of each triangular inlet is directed laterally ■ lateral and anterior branches of the fourth to sixth inter
and is formed by the medial margin of the coracoid process, costal nerves carry general sensation from the skin of
which extends anteriorly from the superior margin of the the breast.
scapula.
The base of the axillary inlet’s triangular opening is the
lateral margin of rib I. KEY FEATURES
Large blood vessels passing between the axillary inlet
and superior thoracic aperture do so by passing over Vertebral level TIV/V
rib I. When working with patients, physicians use vertebral
Proximal parts of the brachial plexus also pass between levels to determine the position of important anatomical
the neck and upper limb by passing through the axillary structures within body regions.
inlet.

Inferior vena cava
Abdomen Esophagus
The diaphragm separates the thorax from the abdomen. Caval opening Aorta
Structures that pass between the thorax and abdomen (vertebral level TVIII)
Central tendon
either penetrate the diaphragm or pass posteriorly to it of diaphragm
(Fig. 3.8):

■ the inferior vena cava pierces the central tendon of
the diaphragm to enter the right side of the mediasti
num near vertebral level TVIII;
■ the esophagus penetrates the muscular part of the
diaphragm to leave the mediastinum and enter the
abdomen just to the left of the midline at vertebral
level TX;
■ the aorta passes posteriorly to the diaphragm at the
midline at vertebral level TXII;
■ numerous other structures that pass between the
thorax and abdomen pass through or posterior to the
diaphragm.

Breast LI
Esophageal hiatus
The breasts, consisting of secretory glands, superficial Aortic hiatus (vertebral level TX)
fascia, and overlying skin, are in the pectoral region on (vertebral level TXII)
each side of the anterior thoracic wall (Fig. 3.9).
Branches from the internal thoracic arteries and veins
Fig. 3.8 Major structures passing between abdomen and thorax.
3-10 perforate the anterior chest wall on each side of the ster


Conceptual overview • Key features 3
A

Axillary process

Axillary
lymph nodes
B
Internal
thoracic artery Pectoralis major

Second, third, and fourth
perforating branches of
internal thoracic artery

Parasternal
lymph nodes

Lactiferous
sinuses
Fourth thoracic
intercostal nerve Lactiferous
ducts
Secretory glands

Lymphatic vessel Deep (pectoral) fascia

Fig. 3.9 Right breast.

Superior mediastinum Trachea

Aortic arch
Rib II
Sternal angle
The horizontal plane passing through the disc that sepa TIV
rates thoracic vertebrae TIV and TV is one of the most sig
nificant planes in the body (Fig. 3.10) because it:

■ passes through the sternal angle anteriorly, marking
the position of the anterior articulation of the costal TV

cartilage of rib II with the sternum. The sternal angle is
used to find the position of rib II as a reference for count
ing ribs (because of the overlying clavicle, rib I is not
palpable);
■ separates the superior mediastinum from the inferior
mediastinum and marks the position of the superior
limit of the pericardium;
■ marks where the arch of the aorta begins and ends; Inferior
mediastinum
■ passes through the site where the superior vena cava
penetrates the pericardium to enter the heart;
■ is the level at which the trachea bifurcates into right
and left main bronchi; and
■ marks the superior limit of the pulmonary trunk. Fig. 3.10 Vertebral level TIV/V. 3-11


Thorax

left upper limb, and part of the left thoracic wall into the
Venous shunts from left to right superior vena cava.
The right atrium is the chamber of the heart that receives The hemiazygos and accessory hemiazygos veins
deoxygenated blood returning from the body. It lies on the drain posterior and lateral parts of the left thoracic wall,
right side of the midline, and the two major veins, the supe pass immediately anterior to the bodies of thoracic ver
rior and inferior venae cavae, that drain into it are also tebrae, and flow into the azygos vein on the right side,
located on the right side of the body. This means that, to which ultimately connects with the superior vena
get to the right side of the body, all blood coming from the cava.
left side has to cross the midline. This lefttoright shunting
is carried out by a number of important and, in some cases, Segmental neurovascular supply
very large, veins, several of which are in the thorax
(Fig. 3.11). of thoracic wall
In adults, the left brachiocephalic vein crosses the The arrangement of vessels and nerves that supply the
midline immediately posterior to the manubrium and thoracic wall reflects the segmental organization of the
delivers blood from the left side of the head and neck, the wall. Arteries to the wall arise from two sources:

Left internal
jugular vein

Left
brachiocephalic
vein

Superior vena cava Intercostal vein

Right atrium Accessory
hemiazygos vein

Azygos vein

Hemiazygos vein

Inferior vena cava

3-12 Fig. 3.11 Left-to-right venous shunts.


■ the thoracic aorta, which is in the posterior mediasti (the anterior rami of thoracic spinal nerves), which inner
num; and vate the wall, related parietal pleura, and associated skin.
■ a pair of vessels, the internal thoracic arteries, which The position of these nerves and vessels relative to the ribs
run along the deep aspect of the anterior thoracic wall must be considered when passing objects, such as chest
on either side of the sternum. tubes, through the thoracic wall.
Dermatomes of the thorax generally reflect the segmen
Posterior and anterior intercostal vessels branch seg tal organization of the thoracic spinal nerves (Fig. 3.12B).
mentally from these arteries and pass laterally around The exception occurs, anteriorly and superiorly, with the
the wall, mainly along the inferior margin of each rib (Fig. first thoracic dermatome, which is located mostly in the
3.12A). Running with these vessels are intercostal nerves upper limb, and not on the trunk.

A Left common carotid artery
Right subclavian artery

Internal thoracic arteries

Arch of aorta

Lateral
cutaneous branch

Posterior
intercostal artery

Anterior
intercostal artery

Anterior
cutaneous branch

Intercostal nerve

Fig. 3.12 A. Segmental neurovascular supply of thoracic wall. 3-13


Thorax

B C

Supraclavicular nerves
T2 T2
T3
T3
T4
T4
T5
Xiphoid process T5
T2 T6 T6
T7 T7
T8 Costal margin
T8
T1 T9 T9
T10 Umbilicus T10
T11 T11
Anterior superior iliac spine
T12 T12

Inguinal ligament

Pubic tubercles

Fig. 3.12, cont’d B. Anterior view of thoracic dermatomes associated with thoracic spinal nerves. C. Lateral view of dermatomes associated
with thoracic spinal nerves.

The anterosuperior region of the trunk receives branches allow movement, and because of the shape and orientation
from the anterior ramus of C4 via supraclavicular branches of the ribs (Fig. 3.14).
of the cervical plexus. A rib’s posterior attachment is superior to its anterior
The highest thoracic dermatome on the anterior chest attachment. Therefore, when a rib is elevated, it moves the
wall is T2, which also extends into the upper limb. In the anterior thoracic wall forward relative to the posterior
midline, skin over the xiphoid process is innervated by T6. wall, which is fixed. In addition, the middle part of each rib
Dermatomes of T7 to T12 follow the contour of the ribs is inferior to its two ends, so that when this region of the
onto the anterior abdominal wall (Fig. 3.12C). rib is elevated, it expands the thoracic wall laterally. Finally,
because the diaphragm is muscular, it changes the volume
of the thorax in the vertical direction.
Sympathetic system Changes in the anterior, lateral, and vertical dimen
All preganglionic nerve fibers of the sympathetic system sions of the thoracic cavity are important for
are carried out of the spinal cord in spinal nerves T1 to L2 breathing.
(Fig. 3.13). This means that sympathetic fibers found any
where in the body ultimately emerge from the spinal cord
as components of these spinal nerves. Preganglionic sym Innervation of the diaphragm
pathetic fibers destined for the head are carried out of the The diaphragm is innervated by two phrenic nerves that
spinal cord in spinal nerve T1. originate, one on each side, as branches of the cervical
plexus in the neck (Fig. 3.15). They arise from the anterior
Flexible wall and inferior rami of cervical nerves C3, C4, and C5, with the major
contribution coming from C4.
thoracic aperture The phrenic nerves pass vertically through the neck,
The thoracic wall is expandable because most ribs articu the superior thoracic aperture, and the mediastinum
3-1 late with other components of the wall by true joints that to supply motor innervation to the entire diaphragm,



Paravertebral
sympathetic trunk Gray ramus Spinal cord
communicans
T1 Spinal nerve

Spinal cord

Spinal nerve

Thoracic sympathetic
ganglion

Sympathetic trunk White ramus
communicans
L2

Elevation of lateral aspect Sternum moves forward
of ribs in inspiration in inspiration because of
rib elevation

Fig. 3.13 Sympathetic trunks.

including the crura (muscular extensions that attach the
diaphragm to the upper lumbar vertebrae). In the medias
tinum, the phrenic nerves pass anteriorly to the roots of the
lungs.
The tissues that initially give rise to the diaphragm are
in an anterior position on the embryological disc before
the head fold develops, which explains the cervical origin
of the nerves that innervate the diaphragm. In other
words, the tissue that gives rise to the diaphragm
originates superior to the ultimate location of the Diaphragm descends to
diaphragm. increase thoracic capacity
in inspiration
Spinal cord injuries below the level of the origin
of the phrenic nerve do not affect movement of the
Fig. 3.14 Flexible thoracic wall and inferior thoracic aperture.
diaphragm. 3-1


Thorax

C3

C4
C5

Right phrenic nerve Left phrenic nerve

Pericardial branch
of phrenic nerve

Pericardium

Diaphragm

Fig. 3.15 Innervation of the diaphragm.

3-1


Regional anatomy • Pectoral region 3

Regional anatomy
The cylindrical thorax consists of: regions, this condenses to form welldefined ligaments,
the suspensory ligaments of breast, which are continu
■ a wall; ous with the dermis of the skin and support the breast.
■ two pleural cavities; Carcinoma of the breast creates tension on these ligaments,
■ the lungs; and causing pitting of the skin.
■ the mediastinum. In nonlactating women, the predominant component of
the breasts is fat, while glandular tissue is more abundant
The thorax houses the heart and lungs, acts as a conduit in lactating women.
for structures passing between the neck and the abdomen, The breast lies on deep fascia related to the pectoralis
and plays a principal role in breathing. In addition, the major muscle and other surrounding muscles. A layer of
thoracic wall protects the heart and lungs and provides loose connective tissue (the retromammary space) sepa
support for the upper limbs. Muscles anchored to the rates the breast from the deep fascia and provides some
anterior thoracic wall provide some of this support, and degree of movement over underlying structures.
together with their associated connective tissues, nerves, The base, or attached surface, of each breast extends
and vessels, and the overlying skin and superficial fascia, vertically from ribs II to VI, and transversely from the
define the pectoral region. sternum to as far laterally as the midaxillary line.
It is important for clinicians to remember when evaluat
ing the breast for pathology that the upper lateral region
PECTORAL REGION of the breast can project around the lateral margin of the
pectoralis major muscle and into the axilla. This axillary
The pectoral region is external to the anterior thoracic wall process (axillary tail) may perforate deep fascia and extend
and anchors the upper limb to the trunk. It consists of: as far superiorly as the apex of the axilla.

■ a superficial compartment containing skin, superficial Arterial supply
fascia, and breasts; and The breast is related to the thoracic wall and to structures
■ a deep compartment containing muscles and associ associated with the upper limb; therefore, vascular supply
ated structures. and drainage can occur by multiple routes (Fig. 3.16):

Nerves, vessels, and lymphatics in the superficial com ■ laterally, vessels from the axillary artery—superior tho
partment emerge from the thoracic wall, the axilla, and the racic, thoracoacromial, lateral thoracic, and subscap
neck. ular arteries;
■ medially, branches from the internal thoracic artery;
■ the second to fourth intercostal arteries via branches
Breast that perforate the thoracic wall and overlying
The breasts consist of mammary glands and associated muscle.
skin and connective tissues. The mammary glands are
modified sweat glands in the superficial fascia anterior
to the pectoral muscles and the anterior thoracic wall Venous drainage
(Fig. 3.16). Veins draining the breast parallel the arteries and ulti
The mammary glands consist of a series of ducts and mately drain into the axillary, internal thoracic, and inter
associated secretory lobules. These converge to form 15 to costal veins.
20 lactiferous ducts, which open independently onto the
nipple. The nipple is surrounded by a circular pigmented Innervation
area of skin termed the areola. Innervation of the breast is via anterior and lateral cutane
A welldeveloped, connective tissue stroma surrounds ous branches of the second to sixth intercostal nerves. The
the ducts and lobules of the mammary gland. In certain nipple is innervated by the fourth intercostal nerve. 3-1


Thorax

Internal thoracic artery

Pectoral branch of
thoracoacromial artery Pectoralis major muscle

Apical axillary nodes

Central axillary nodes

Secretory lobules
Lateral thoracic artery
Suspensory ligaments

Lateral axillary nodes Lactiferous ducts

Pectoral axillary nodes
Lactiferous sinuses

Axillary process Retromammary space

Parasternal nodes
Lymphatic and venous drainage
passes from lateral and superior
part of the breast into axilla

Mammary branches of
Areola internal thoracic artery

Lymphatic and venous
drainage passes from medial part
Secretory of the breast parasternally
lobules
Lymphatic and venous
drainage passes from inferior part
of the breast into the abdomen

Fig. 3.16 Breasts.

Lymphatic drainage Axillary nodes drain into the subclavian trunks, para
Lymphatic drainage of the breast is as follows: sternal nodes drain into the bronchomediastinal trunks,
and intercostal nodes drain either into the thoracic duct or
■ approximately 75% is via lymphatic vessels that drain into the bronchomediastinal trunks.
laterally and superiorly into axillary nodes (Fig. 3.16);
■ most of the remaining drainage is into parasternal
nodes deep to the anterior thoracic wall and associated
with the internal thoracic artery; and Breast in men
■ some drainage may occur via lymphatic vessels that The breast in men is rudimentary and consists only of
follow the lateral branches of posterior intercostal small ducts, often composed of cords of cells, that normally
arteries and connect with intercostal nodes situated do not extend beyond the areola. Breast cancer can occur
3-1 near the heads and necks of ribs. in men.


Regional anatomy • Pectoral region 3
In the clinic

Breast cancer Further imaging may include bone scanning using
Breast cancer is one of the most common radioactive isotopes, which are avidly taken up by the
malignancies in women. In the early stages, curative tumor metastases in bone.
treatment may include surgery, radiotherapy, and Lymph drainage of the breast is complex. Lymph
chemotherapy. vessels pass to axillary, supraclavicular, parasternal, and
Breast cancer develops in the cells of the acini, abdominal lymph nodes, as well as the opposite breast.
lactiferous ducts, and lobules of the breast. Tumor Containment of nodal metastatic breast cancer is
growth and spread depends on the exact cellular site of therefore potentially difficult because it can spread
origin of the cancer. These factors affect the response to through many lymph node groups.
surgery, chemotherapy, and radiotherapy. Breast tumors Subcutaneous lymphatic obstruction and tumor
spread via the lymphatics and veins, or by direct growth pull on connective tissue ligaments in the breast
invasion. resulting in the appearance of an orange peel texture
When a patient has a lump in the breast, a diagnosis of (peau d’orange) on the surface of the breast. Further
breast cancer is confirmed by a biopsy and histological subcutaneous spread can induce a rare manifestation of
evaluation. Once confirmed, the clinician must attempt to breast cancer that produces a hard, woody texture to the
stage the tumor. skin (cancer en cuirasse).
Staging the tumor means defining the: A mastectomy (surgical removal of the breast) involves
excision of the breast tissue to the pectoralis major muscle
■ size of the primary tumor;
and fascia. Within the axilla the breast tissue must be
■ exact site of the primary tumor;
removed from the medial axillary wall. Closely applied to
■ number and sites of lymph node spread; and
the medial axillary wall is the long thoracic nerve. Damage
■ organs to which the tumor may have spread.
to this nerve can result in paralysis of the serratus anterior
Computed tomography (CT) scanning of the body may muscle producing a characteristic “winged” scapula. It is
be carried out to look for any spread to the lungs also possible to damage the nerve to the latissimus dorsi
(pulmonary metastases), liver (hepatic metastases), or muscle, and this may affect extension, medial rotation,
bone (bony metastases). and adduction of the humerus.

Muscles of the pectoral region Pectoralis major adducts, flexes, and medially rotates
Each pectoral region contains the pectoralis major, pecto the arm.
ralis minor, and subclavius muscles (Fig. 3.17 and Table
3.1). All originate from the anterior thoracic wall and Subclavius and pectoralis minor
insert into bones of the upper limb. The subclavius and pectoralis minor muscles underlie
pectoralis major:
Pectoralis major
The pectoralis major muscle is the largest and most ■ subclavius is small and passes laterally from the ante
superficial of the pectoral region muscles. It directly rior and medial part of rib I to the inferior surface of the
underlies the breast and is separated from it by deep fascia clavicle;
and the loose connective tissue of the retromammary ■ pectoralis minor passes from the anterior surfaces of
space. ribs III to V to the coracoid process of the scapula.
Pectoralis major has a broad origin that includes the
anterior surfaces of the medial half of the clavicle, the Both subclavius and pectoralis minor pull the tip of the
sternum, and related costal cartilages. The muscle shoulder inferiorly.
fibers converge to form a flat tendon, which inserts A continuous layer of deep fascia, clavipectoral fascia,
into the lateral lip of the intertubercular sulcus of the encloses subclavius and pectoralis minor and attaches to
humerus. the clavicle above and to the floor of the axilla below. 3-1


Thorax

Subclavius
Lateral pectoral nerve

Pectoralis major
Thoracoacromial artery

Pectoralis minor
Medial pectoral nerve
Lateral thoracic artery

Clavipectoral fascia

Fig. 3.17 Muscles and fascia of the pectoral region.

Table 3.1 Muscles of the pectoral region

Muscle Origin Insertion Innervation Function
Pectoralis major Medial half of clavicle and anterior surface of Lateral lip of Medial and Adduction, medial rotation, and
sternum, first seven costal cartilages, intertubercular lateral pectoral flexion of the humerus at the
aponeurosis of external oblique sulcus of humerus nerves shoulder joint
Subclavius Rib I at junction between rib and costal Groove on inferior Nerve to Pulls clavicle medially to stabilize
cartilage surface of middle subclavius sternoclavicular joint
third of clavicle
Pectoralis minor Anterior surfaces of the third, fourth and Coracoid process of Medial pectoral Depresses tip of shoulder;
fifth ribs, and deep fascia overlying the scapula nerves protracts scapula
related intercostal spaces

The muscles of the pectoral region form the anterior pectoral region and the axilla pass through the clavipec
wall of the axilla, a region between the upper limb and toral fascia between subclavius and pectoralis minor or
the neck through which all major structures pass. pass under the inferior margins of pectoralis major and
Nerves, vessels, and lymphatics that pass between the minor.
3-20


Regional anatomy • Thoracic wall 3
Anterior
Superior articular process

Facet for articulation Superior
Vertebral body with tubercle of rib

Superior demifacet

Vertebral
Posterior Anterior
foramen
Pedicle

Inferior
Spinous process Lamina
Facet for articulation Transverse process Inferior articular process Demifacets for articulation
with tubercle of rib with head of ribs
Posterior

Superior view Superolateral view

Fig. 3.18 Typical thoracic vertebra.

THORACIC WALL (Fig. 3.18). The vertebral foramen is generally circular
and the laminae are broad and overlap with those of the
The thoracic wall is segmental in design and composed of vertebra below. The superior articular processes are
skeletal elements and muscles. It extends between: flat, with their articular surfaces facing almost directly pos
teriorly, while the inferior articular processes project
■ the superior thoracic aperture bordered by vertebra TI, from the laminae and their articular facets face anteriorly.
rib I, and the manubrium of sternum; and The transverse processes are club shaped and project
■ the inferior thoracic aperture bordered by vertebra posterolaterally.
TXII, rib XII, the end of rib XI, the costal margin, and
the xiphoid process of sternum.
Articulation with ribs
A typical thoracic vertebra has three sites on each side for
Skeletal framework articulation with ribs.
The skeletal elements of the thoracic wall consist of tho
racic vertebrae, intervertebral discs, ribs, and sternum.
■ Two demifacets (i.e., partial facets) are located on the
Thoracic vertebrae superior and inferior aspects of the body for articulation
There are twelve thoracic vertebrae, each of which is with corresponding sites on the heads of adjacent ribs.
characterized by articulations with ribs. The superior costal facet articulates with part of the
head of its own rib, and the inferior costal facet artic
A typical thoracic vertebra ulates with part of the head of the rib below.
A typical thoracic vertebra has a heartshaped vertebral ■ An oval facet (transverse costal facet) at the end of
body, with roughly equal dimensions in the transverse the transverse process articulates with the tubercle of
and anteroposterior directions, and a long spinous process its own rib.
3-21


Thorax

Not all vertebrae articulate with ribs in the same fashion of its own rib—in other words, the head of rib I does not
(Fig. 3.19): articulate with vertebra CVII;
■ similarly, vertebra TX (and often TIX) articulates only
■ the superior costal facets on the body of vertebra TI are with its own ribs and therefore lacks inferior demifacets
complete and articulate with a single facet on the head on the body;
■ vertebrae TXI and TXII articulate only with the heads
of their own ribs—they lack transverse costal facets and
have only a single complete facet on each side of their
bodies.
Vertebra TI
Ribs
There are twelve pairs of ribs, each terminating anteriorly
in a costal cartilage (Fig. 3.20).
Although all ribs articulate with the vertebral column,
only the costal cartilages of the upper seven ribs, known
as true ribs, articulate directly with the sternum. The
remaining five pairs of ribs are false ribs:
Superior costal facet for head of rib I
■ the costal cartilages of ribs VIII to X articulate anteri
orly with the costal cartilages of the ribs above;
■ ribs XI and XII have no anterior connection with other
ribs or with the sternum and are often called floating
ribs.

Vertebra TX

True ribs I–VII Intercostal space

Costal cartilage

Single complete costal facet for head of rib X

Vertebra TXI

False ribs VIII–XII Floating ribs

No costal facet on transverse process
Costal margin

Fig. 3.19 Typical thoracic vertebrae. Fig. 3.20 Ribs.
3-22


A typical rib consists of a curved shaft with anterior and The shaft is generally thin and flat with internal and
posterior ends (Fig. 3.21). The anterior end is continuous external surfaces.
with its costal cartilage. The posterior end articulates with The superior margin is smooth and rounded, whereas
the vertebral column and is characterized by a head, neck, the inferior margin is sharp. The shaft bends forward just
and tubercle. laterally to the tubercle at a site termed the angle. It also
The head is somewhat expanded and typically presents has a gentle twist around its longitudinal axis so that the
two articular surfaces separated by a crest. The smaller internal surface of the anterior part of the shaft faces some
superior surface articulates with the inferior costal facet on what superiorly relative to the posterior part. The inferior
the body of the vertebra above, whereas the larger inferior margin of the internal surface is marked by a distinct
facet articulates with the superior costal facet of its own costal groove.
vertebra.
The neck is a short flat region of bone that separates
the head from the tubercle. Distinct features of upper and
The tubercle projects posteriorly from the junction of lower ribs
the neck with the shaft and consists of two regions, an The upper and lower ribs have distinct features (Fig.
articular part and a nonarticular part: 3.22).

■ the articular part is medial and has an oval facet for Rib I
articulation with a corresponding facet on the trans Rib I is flat in the horizontal plane and has broad superior
verse process of the associated vertebra; and inferior surfaces. From its articulation with vertebra
■ the raised nonarticular part is roughened by ligament TI, it slopes inferiorly to its attachment to the manubrium
attachments. of sternum. The head articulates only with the body of

Rib I
Head Neck
Tubercle
A
Posterior Tubercle
Angle
Head

Neck
Internal surface
Scalene
tubercle
Costal
groove Grooves

Costal cartilage

External surface
Anterior
Costal
B Neck cartilage
Tubercle

Crest
Rib XII

Non-articular surface Articular facets
Articular facet

Fig. 3.21 A typical rib. A. Anterior view. B. Posterior view of
proximal end of rib. Fig. 3.22 Atypical ribs.
3-23


Thorax

vertebra TI and therefore has only one articular surface. Articular site Jugular notch
Like other ribs, the tubercle has a facet for articulation with for clavicle
the transverse process. The superior surface of the rib is Manubrium of
sternum
characterized by a distinct tubercle, the scalene tubercle,
which separates two smooth grooves that cross the rib
approximately midway along the shaft. The anterior Attachment Sternal angle
site for rib I (manubriosternal
groove is caused by the subclavian vein, and the posterior
joint)
groove is caused by the subclavian artery. Anterior and
posterior to these grooves, the shaft is roughened by Articular
muscle and ligament attachments. demifacets
for rib II
Rib II
Rib II, like rib I, is flat but twice as long. It articulates with
the vertebral column in a way typical of most ribs. Transverse
ridges
Rib X
The head of rib X has a single facet for articulation with
its own vertebra. Articular facets for
ribs III –VI Body of
Ribs XI and XII sternum

Ribs XI and XII articulate only with the bodies of their
own vertebrae and have no tubercles or necks. Both
ribs are short, have little curve, and are pointed
anteriorly.
Articular facets
Sternum for rib VII
Xiphoid
The adult sternum consists of three major elements: the process
broad and superiorly positioned manubrium of sternum,
the narrow and longitudinally oriented body of sternum, Fig. 3.23 Sternum.
and the small and inferiorly positioned xiphoid process
(Fig. 3.23).

Manubrium of sternum
The manubrium of sternum forms part of the bony
framework of the neck and the thorax. The lateral margins of the body of the sternum have
The superior surface of the manubrium is expanded articular facets for costal cartilages. Superiorly, each lateral
laterally and bears a distinct and palpable notch, the margin has a demifacet for articulation with the inferior
jugular notch (suprasternal notch), in the midline. aspect of the second costal cartilage. Inferior to this demi
On either side of this notch is a large oval fossa for articu facet are four facets for articulation with the costal carti
lation with the clavicle. Immediately inferior to this fossa, lages of ribs III to VI.
on each lateral surface of the manubrium, is a facet for At the inferior end of the body of the sternum is a demi
the attachment of the first costal cartilage. At the lower facet for articulation with the upper demifacet on the
end of the lateral border is a demifacet for articulation seventh costal cartilage. The inferior end of the body of the
with the upper half of the anterior end of the second sternum is attached to the xiphoid process.
costal cartilage.
Xiphoid process
Body of the sternum The xiphoid process is the smallest part of the sternum.
The body of the sternum is flat. Its shape is variable: it may be wide, thin, pointed, bifid,
The anterior surface of the body of the sternum is often curved, or perforated. It begins as a cartilaginous struc
marked by transverse ridges that represent lines of fusion ture, which becomes ossified in the adult. On each side of
between the segmental elements called sternebrae, from its upper lateral margin is a demifacet for articulation with
3-2 which this part of the sternum arises embryologically. the inferior end of the seventh costal cartilage.


intervertebral disc and separates the two articular surfaces
Joints
on the head of the rib. The two synovial compartments and
Costovertebral joints the intervening ligament are surrounded by a single joint
A typical rib articulates with: capsule attached to the outer margins of the combined
articular surfaces of the head and vertebral column.
■ the bodies of adjacent vertebrae, forming a joint with
the head of the rib; and Costotransverse joints
■ the transverse process of its related vertebra, forming a Costotransverse joints are synovial joints between the
costotransverse joint (Fig. 3.24). tubercle of a rib and the transverse process of the related
vertebra (Fig. 3.24). The capsule surrounding each joint is
Together, the costovertebral joints and related liga thin. The joint is stabilized by two strong extracapsular liga
ments allow the necks of the ribs either to rotate around ments that span the space between the transverse process
their longitudinal axes, which occurs mainly in the upper and the rib on the medial and lateral sides of the joint:
ribs, or to ascend and descend relative to the vertebral
column, which occurs mainly in the lower ribs. The com ■ the costotransverse ligament is medial to the joint
bined movements of all of the ribs on the vertebral column and attaches the neck of the rib to the transverse
are essential for altering the volume of the thoracic cavity process;
during breathing. ■ the lateral costotransverse ligament is lateral to the
joint and attaches the tip of the transverse process to
Joint with head of rib the roughened nonarticular part of the tubercle of
The two facets on the head of the rib articulate with the the rib.
superior facet on the body of its own vertebra and with the
inferior facet on the body of the vertebra above. This joint A third ligament, the superior costotransverse liga-
is divided into two synovial compartments by an intra ment, attaches the superior surface of the neck of the rib
articular ligament, which attaches the crest to the adjacent to the transverse process of the vertebra above.

Vertebra

Joint capsule

Superior Rib
costotransverse ligament Disc

Intra-articular
ligament

Vertebra
Joint
cavities

Costotransverse
ligament

Lateral
costotransverse
ligament
Joint with vertebral body

Costotransverse joint

Fig. 3.24 Costovertebral joints.
3-2


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