The document provides a comprehensive overview of the anatomy of the thorax, including the thoracic cage, its components such as ribs, sternum, and vertebrae, as well as the muscles and neurovascular structures associated with the thoracic wall. It elaborates on the mediastinum's divisions and contents, detailing the structure of the breast and diaphragm, their blood supply, and lymphatic drainage. Additionally, it addresses clinical aspects including chest deformities and the development and anomalies of mammary glands.

1. Dr S M Niazur Rahman
Anatomy Unit, Faculty of Medicine
L 18: THORAX
ANATOMY L 18: MBBS B 21: Element 1: 07.12.2015

2. Learning outcomes
• List and describe the bones and muscles of
thoracic cage and wall.
• Discuss the contents of intercostal space.
• Describe the boundaries,subdivisions and
contents of mediastinum.
• Explain the structure,blood supply and
lymphatic drainage of breast.
• Describe the origin, insertion, nerve supply,
major openings and action of diaphragm.

3.  Thoracic cage
 Thoracic wall
 Mediastinum
 Breast
 Diaphragm
Thorax

4. Thoracic cage
Made up of bones
• Ribs – 12 pairs.
• Sternum – manubrium,
body & xiphoid.
• Vertebral column – 12
thoracic vertebrae.

5. • Classification:
- True & false
- Typical & atypical
• True and false ribs:
-True ribs: 1-7, as they are
connected to the sternum
through their respective
cartilages.(vertebro sternal ribs).
- False ribs: 8, 9, 10, 11, 12.
Connected to next higher
cartilages to reach sternum but
11, 12 are free in the anterior
ends, called floating ribs.
• Typical ribs: 3 – 9
• Atypical ribs: 1,2 & 10, 11, 12
Bones of Thorax: Ribs

6. Parts of typical rib: Anterior, posterior ends & shaft.
Anterior end: Oval, concave articulates with costal
cartilage.
Posterior end:
- head with 2 facets articulating with the body of
thoracic vertebra.
- small neck & tubercle: junction of neck & shaft;
articulates with transverse process of thoracic vertebra.
Shaft: 2 surfaces (outer and inner) & angle. Inner aspect,
above the inferior border- Costal groove containing
Neuro-vascular bundle (ICV, ICA, ICN).
Bones of Thorax: Ribs

7. Parts of vertebra:
• Body: heart-shaped
• Vertebral or Neural arch:
- Pedicle
- Transverse process
- Lamina
- Spinous process and
- Articulating facets
-Vertebral canal for spinal cord
 12 in number: Typical- 2 to 8 &
Atypical- 1,9,10,11 & 12.
 Has articulating surfaces/
costal facet on the body and
transverse processes for the
ribs.
Bones of Thorax: Thoracic vertebra

8. • Sternum is a flat bone, present in front of
the thoracic cage.
• Parts: Manubrium, Body & Xiphoid
process.
• Manubrium:
- Upper part of the sternum.
- Joins with medial end of clavicle and first
costal cartilage.
-Has jugular or interclavicular or
suprasternal notch.
Body : Larger part of the sternum. On each
side, it receives ribs through their costal
cartilages (3rd to 6th rib).
Xiphoid process: Most variable part of the
sternum. Cartilaginous structure in adults.
Bones of Thorax: Sternum

9. Thoracic Cage: Applied Anatomy
Funnel chest: Lower end of
sternum is depressed and xiphoid
process projects forwards.
Rickets: Pigeon chest associated
with lack of calcification in the costal
cartilages at the costo-chondral
junction.
Barrel shaped chest: In chronic
obstructive pulmonary disease
(COPD)- asthma & emphysema.
Funnel chest
Barrel chest
Pigeon chest

10. • Thoracic cage is formed by bony frame work.
• Bones include sternum anteriorly,12 pairs of ribs laterally
& posteriorly and 12 thoracic vertebrae posteriorly.
• Sternum has manubrium,body & xiphoid process.
• Ribs have head, neck & shaft.
• Vertebra has body, pedicle, transverse process and
spine.
Thoracic Cage: Summary

11. Thoracic Wall
• Skeletal frame work.
• Intercostal spaces filled with
intercostal muscles, intercostal
nerves, arteries and veins.
• Intercostal muscles:
1.External intercostal
2.Internal intercostal
3.Transversus thoracis : 3 parts
- Subcostalis,
- Intercostalis intimi
- Sternocostalis.

12. 1. External intercostal muscles:
• Extends from the tubercle of rib
posteriorly to costo chondral
junction anteriorly.
• Between costochondral junction
and the sternum the muscle is
replaced by external intercostal
membrane.
• Origin:From the lower border of
rib.
• Insertion:Into the upper border of
the rib.
• Direction of fibres- downwards,
forwards and medially.
Thoracic Wall: Intercostal muscles

13. 2. Internal intercostal muscle:
• Extends from the lateral
border of sternum to angle of
rib. Beyond the angle the
muscle is replaced by
posterior or internal
intercostal membrane.
• Origin: From the lower border
of rib.
• Insertion: Into the upper
border of the rib.
• Direction of fibres-
downwards, backwards and
laterally at right angles to the
external intercostalis.
Thoracic Wall: Intercostal muscles

14. 3. Transversus thoracis: 3 parts-
- Sternocostalis – present in the
anterior parts of upper intercostal
spaces.
- Subcostalis - confined to the
posterior part of lower intercostal
spaces.
- Intercostalis intimi or innermost
intercostal: present in the middle
third of the intercostal spaces.
Direction of fibres is similar to
internal intercostal.
Thoracic Wall: Intercostal muscles

15. • Nerve supply:
Intercostal nerves.
• Action:
- Prevent retraction of intercostal spaces during
expiration, bulging outwards during inspiration.
- Portion of external & internal intercostal
muscles elevate the ribs during inspiration.
- Internal intercostal and transverse thoracis
depress the ribs during expiration.
Thoracic Wall: Intercostal muscles

16. • Neurovascular bundle consists of intercostal vein,
intercostal artery and intercostal nerve (VAN).
• Neurovascular plane lying between the internal intercostal
and innermost intercostal muscles.
Thoracic Wall: Intercostal spaces

17. • 11 pairs of intercostal and 1
pair of subcostal nerves.
• Origin:Ventral rami of
thoracic spinal nerves.
• Course:Passes from
posterior to anterior in the
costal groove in the
neurovascular plane.
• Branches:
1. Lateral cutaneous
2. Anterior cutaneous
3. Muscular branches.
Thoracic Wall: Intercostal nerve

18. • Each intercostal space
contains 1 posterior & 2
anterior intercostal arteries.
• Posterior intercostal arteries
arise from costocervical
artery and thoracic aorta.
• Anterior intercostal arteries
arise from internal thoracic
artery.
Thoracic Wall: Intercostal artery

19. • Each intercostal space
contains 1 posterior and 2
anterior intercostal veins.
• Posterior intercostal veins
drain into:
- Right side -right
brachiocephalic vein
and azygos vein.
- Left side - left
brachiocephalic vein,
hemiazygos and accessory
hemiazygos vein.
• Anterior intercostal veins
drain into internal thoracic
vein.
Thoracic Wall: Intercostal vein

20. • Paracentesis thoracis-removal
of fluid from the pleural cavity.
• Needle is inserted into the
middle of the intercostal space.
• Intercostal nerve block at the
intercostal groove.
• Pus from the thoracic bodies
tracks along the neurovascular
bundle and point of termination
of the intercostal nerve.
• Herpes Zoster – viral disease,
affects thoracic ganglia leading
painful vesicles all along the
intercostal nerve distribution.
Thoracic Wall: Applied Anatomy

21. Mediastinum

22. • Septum or space between
the two lungs in the thoracic
cavity.
• Boundaries:
Anterior: sternum.
Posterior: Thoracic vertebral
column.
Superior: Thoracic inlet.
Inferior: Diaphragm.
Lateral: Mediastinal pleura
(both sides).
Mediastinum

23. Mediastinum
• Divisions: imaginary line
passing at sternal angle -T4
divides it into superior & inferior
mediastinum
• Inferior mediastinum is further
divided into:
- Anterior: Area in front of
pericardium.
- Middle: Area with pericardium
& its contents.
- Posterior: Area behind
pericardium.

24. Boundaries –
Anterior: Manubrium sterni.
Posterior: T4 upper portion.
Superior: Thoracic inlet.
Inferior: Imaginary line at sternal
angle – T4 behind.
Superior mediastinum

25. Contents:
• Trachea & oesophagus.
• Muscles: sternohyoid, sternothyroid.
• Arteries: Arch of aorta, brachiocephalic artery, left
common carotid artery, left subclavian artery.
• Veins: Right & left brachiocephalic veins, SVC (upper
part), left superior intercostal vein.
• Nerves: Vagus, phrenic, cardiac N (both sides),left
recurrent laryngeal nerve.
• Thymus.
• Thoracic duct .
• Lymph nodes: Paratracheal, brachiocephalic and
tracheobronchial.
Superior mediastinum

26. • Narrow space in front of pericardium,
overlapped by thin anterior borders of lung.
• Continuous with pretracheal space of the
neck.
• Boundaries:
Anterior: Body of sternum.
Posterior: Pericardium.
Superior: Imaginary plane separating the
superior from inferior mediastinum.
Inferior: Superior surface of diaphragm.
Lateral : Mediastinal pleura (both sides)
• Contents: sternopericardial ligaments,
lymph nodes, branches of internal thoracic
artery, lower part of thymus.
Anterios mediastinum

27. • Pericardium and contents along with
phrenic nerve, percardiophrenic
vessels.
• Contents:
- Heart enclosed with pericardium.
- Arteries: ascending aorta, pulmonary
trunk and two pulmonary arteries.
- Veins: lower part SVC, terminal part of
azygous vein, right & left
pulmonary veins.
- Nerves: phrenic and deep cardiac
plexus.
- Tubes: bifurcation of trachea, right &
left principal bronchi.
Middle mediastinum

28. • Boundaries:
- Anterior: Pericardium,
bifurcation of trachea, pulmonary
vessels and posterior part of
upper surface of diaphragm.
- Posterior: Lower 8 thoracic
vertebrae with discs.
- Lateral: mediastinal pleura
(both sides).
Posterior mediastinum

29. • Contents:
- Oesophagus.
- Arteries: Descending thoracic aorta &
branches.
- Veins: Azygos vein, hemiazygos vein,
Accessory hemiazygos vein.
- Nerves: Vagus, splanchnic, greater & lesser
and least arising from lower 8 thoracic ganglia
of the sympathetic chain.
- Lymph nodes and lymphatics: Posterior
mediastinal nodes along aorta, thoracic duct.
Posterior mediastinum

30. • Modified sweat gland.
• Derived from the epithelium of the skin.
• Males: Rudimentary.
• Females: Well developed after puberty.
• Location:
- Superficial fascia of pectoral region.
- Lies on the pectoralis major, partly on serratus anterior, external
oblique.
• Size: variable.
• Extension:
- 2nd rib – 6th rib along mid clavicular line.
- along 4th rib – on the horizontal plane – margin
of the sternum to mid axillary line.
- extends into axilla – axillary tail of Spence.
Mammary gland / Breast

31. • Nipple is the conical elevation.
• Areola is pigmented area
around the nipple – has
modified sebaceous glands,
which enlarge during
pregnancy – tubercles of
Montgomery that lubricate the
breast during breast feeding.
• Suspensory ligament of
Cooper - fibrous tissue
extends from the skin to the
underlying fascia covering the
muscle –becomes weak in
elderly female and makes it
pendulous (sagging).
Mammary gland / Breast

32. Internal structure:
• 15-20 lobes separated by a
fibrous connective tissue.
• Each lobe drained by –
lactiferous duct.
- ducts from each lobe converge
to open at the summit of
the nipple.
- lactiferous ducts show a
dilatation called – lactiferous
sinus.
Mammary gland / Breast

33. • Arterial supply:
1.Superior thoracic artery- branch of axillary artery –
supplies upper part of the breast.
2.Lateral thoracic artery – branch of axillary artery –
supplies lateral part of the breast.
3. Internal thoracic artery – branch of subclavian
artery – with their medial mammary branch supplies
medial part of the breast .
4. Posterior intercostal artery – arise from thoracic
aorta – lateral part of the gland.
• Venous drainage: Veins drain into internal
thoacic,axillary and posterior intercostal veins.
Mammary gland / Breast

34. • Skin:
- Outer side – axillary group of nodes.
- Upper quadrant – supra clavicular nodes.
- Inner quadrant – internal mammary nodes.
• Parenchyma, nipple and areola:
- Accompany lateral thoracic artery –anterior set of
axillary nodes.
- Posterior sets (few) via axillary tail spence – efferents
to central and apical nodes.
- From medial side and lateral side - internal thoracic
artery – parasternal nodes.
- ateral and posterior side – posterior inter costal nodes.
Mammary gland: Lymphatic drainage

35. Mammary gland: Lymphatic drainage

36. • Anterior and lateral cutaneous branches of the
fourth, fifth, and sixth thoracic nerves(T4,5,6).
• Sensation to the nipple derives largely from
the lateral cutaneous branch of T4.
Mammary gland: Nerve supply

37. • Develops partly from mesoderm and
partly from ectoderm- its blood vessels and
connective tissue from the mesoderm
,cellular elements from the ectoderm.
•During the sixth week of intrauterine
development, the mammary glands
develop as solid down growths of the
epidermis that extend into the
mesenchyme from the axilla to the inguinal
region (milk line).
• Later, these ridges disappear except in
the pectoral area.
Mammary gland: Developement

38. Mammary gland: Anomalies
Amastia (absence of breast) athelia (absence of nipple) and
may occur bilaterally or unilaterally.
Polymastia: Extra breast most commonly occur along the milk
line
Polythelia: Extra nipple
Gynecomastia is a benign and usually self-limited condition that
occurs in 50-60% of boys during early adolescence.
Gynecomastia occurs in Klinefelter syndrome, testicular
feminization, hormone-secreting tumors, hyperthyroidism,
hypothyroidism.

39. • Musculo-tendinous partition between
the thorax and abdomen.
Parts: vertebral, sternal and costal.
Origin:
Verterbral origin:
Right crus: L1,2,3
Left crus: L1,2
Joined by median arcuate ligament.
Costal origin: Inner aspects of lower
six costal cartilages.
Sternal origin: Posterior surface of
xiphoid process.
Insertion: All the 3 parts converge on
central tendon.
Action: Increases the vertical diameter
of the thoracic cavity in inspiration.
Diaphragm

40. • Nerve supply:
- Phrenic nerve (C3, 4, 5) –
motor and sensory to central
part.
- Lower six intercostal nerves –
sensory to peripheral part.
• Major openings in the
diaphragm and structures
passing through diaphragm:
- T12 - aorta, azygos vein, and
thoracic duct.
- T10 - oesophagus, branches of
left gastric artery,vein and vagul
trunks.
- T8 – inferior vena cava, right
phrenic nerve.
Diaphragm

41. Suggested/Further Reading:
1. Essentials of Anatomy-A K Datta (part 1 & 3)
2. B D Chaurasia’s Human Anatomy- volume 1