ANAT 204 Thorax Anatomy

• The lecture is about the gross anatomy of the thorax, part of ANAT 204.
• Professor BALA Usman is the instructor.

Lecture Plan

• Topics to be covered include the thoracic skeleton, muscles, nerves, arteries/veins, and the breast.

Thoracic Wall Components

• The thoracic cage/skeleton
• The muscles covering the anterolateral aspect
• The intercostal muscles
• Subcutaneous tissue

Thoracic Skeleton

• Consists of 12 pairs of ribs and costal cartilage.
• Includes 12 thoracic vertebrae and intervertebral discs.
• The sternum is part of the thoracic skeleton.

Ribs

• Ribs are curved, flat bones with a spongy interior.
• There are three classifications: true, false, and floating.
• There are typical and atypical ribs.

Rib Classification

• True ribs: 1st to 7th ribs, vertebrocostal.
• False ribs: 8th to 10th ribs, vertrbrochondral.
• Floating ribs: 11th and 12th ribs.

Typical Ribs (3rd - 9th) Features

• Head: Features two facets separated by a crest.
• Inferior facet: Articulates with the numerically corresponding vertebrae.
• Superior facet: Articulates with vertebra above it.
• Neck: Connects the head with the body at the level of the tubercle.
• Tubercle: Located at the junction of the neck and the body, articulating with the corresponding transverse process of the vertebra.
• Body: Thin, flat, and curved.
  • Has internal and external surfaces.
  • Internal Surface: Has the costal groove for neurovascular vessels.
  • Costal Angle: The point where the rib turns anterolaterally.

Atypical Ribs

• Includes the 1st, 2nd, 10th-12th ribs.

First Rib Characteristics

• Shortest and broadest rib.
• Has one facet for T1.
• Features two transverse grooves separated by a tubercle.

Second Rib Characteristics

• Thinner and less curved than the 1st rib.
• Longer than the 1st rib.
• Possesses two facets and a tuberosity for the serratus anterior.

Tenth to Twelfth Ribs

• Feature one facet.
• 11th and 12th ribs are short, lack a neck, have little curve, and are pointed anteriorly.

Intercostal Spaces

• There are 11 intercostal spaces.
• Named after the rib that forms the superior border.
• Eleven intercostal nerves occupy them, along with muscles, membranes, and vessels.
• The subcostal space refers to the space below the 12th rib, containing the subcostal nerve.

Thoracic Vertebrae

• There are 12 in number
• Each typical TV has the following:
  • Body bears costal demifacets for articulation with the head of the ribs.
  • Has a long spinous process
  • Features a circular vertebral foramen

Thoracic Vertebrae processes

• Transverse process: Has a facet for articulation with the tubercle of the rib.
• Articular process:
  • Superior: flat and the surface is facing posteriorly.
  • Inferior: faces anteriorly

Specific Thoracic Vertebrae

• T1 has only an inferior costal facet.
• T10 often articulates with its rib and lacks an inferior costal facet.
• T11 and T12 have only one single facet on each side of the body
• Lack transverse costal facets.

Sternum

• It is a flat and elongated bone.
• Lies in the middle of the thoracic cage.
• Has three parts: Manubrium, Body, and Xiphoid process.

Manubrium

• The widest and thickest of the 3 parts of the sternum
• Has jugular notch (suprasternal notch).
• Oval fossa laterally for clavicle.
• Inferior to the oval fossa is the site for articulation of the rib.

Body of Sternum

• Longer, thinner, and narrower than the manubrium.
• Located at the level of T5-T9.
• Features costal notches for articulation with costal cartilage laterally.
• Consists of sternabrae, also known as primodal segments of the sternum.

Xiphoid Process

• Smallest, thin, and elongated sternum part.
• Has a pointed inferior end, lying at the level of T10.
• Cartilaginous in youth but ossifies in adults older than 40 years.

Thoracic Aperture

• Superior thoracic aperture -Oblique, kidney in shape -Measures 6.5 cm anterior-posteriorly and 11 cm transversely in adults. -Posteriorly: Bordered by T1 -Laterally: By the 1st rib and costal cartilage -Anteriorly: By the superior border of the manubrium

Inferior Thoracic Aperture

• Has an irregular outline.
• Posteriorly bordered by T12.
• Posteriolaterally bordered by the 11th and 12th pairs of ribs.
• Anteriolaterally bordered by the costal cartilage of the 7th-10th ribs.
• Anteriorly bordered by the xiphisternal joint.

External Thoracic Wall Muscles

• Serrautus posterior superior
• Serrautus posterior inferior

Intercostal Muscles

• Consists of the external, internal, and innermost intercostal muscles

Internal Muscles

• Subcostal
• Tranversus thoracic

Serratus Posterior Superior

• Originates from the ligamentum nuchae and spinous processes C7-T3.
• Inserts at the superior borders of the 2nd-4th ribs.
• Innervated by 2nd-5th intercostal nerves.
• Function: Elevates the ribs.

Serratus Posterior Inferior

• Originates from the spinous processes T11-L2 vertebrae.
• Inserts at the inferior borders of the 8th-12th ribs near their angle.
• Receives innervation from ventral rami of 9th-12th thoracic spinal nerves.
• Function: Depresses the ribs.

Intercostal Muscles

• Originate from the inferior borders of the rib and insert into the superior borders of the rib below
• All are supplied by the intercostal nerves (T1-T11).

External Intercostal Muscles

• Fibers pass downward and forward (inferioanteriorly).
• Elevates ribs, which increases thoracic volume
• Replaced by the anterior intercostal membrane anteriorly.

Internal Intercostal Muscles

• From the lateral edge of the costal groove
• Fibers pass downwards and backward (inferoposteriorly).
• Reduces thoracic volume by depressing the ribcage
• Elevates the ribs.

Innermost Intercostal

• Originates from the medial edge of the costal groove.
• Fibers pass downwards and backward (inferoposteriorly).
• Reduces thoracic volume by depressing the ribcage.
• Elevates the ribs.

More about Innermost Intercostal Muscles

• Originates from the medial edge of the costal groove and inserts into the superior surface of the rib below.
• Fibers pass transversely.
• Incomplete.

Subcostal Muscles

• Arise from the internal surface of lower ribs near their angles.
• Insert on superior borders of 2nd or 3rd ribs below.
• Innervated by IC nerves and elevate the ribs.

Transversus Thoracic

• Arises from the posterior surface of the lower sternum.
• Inserts at the internal surface of costal cartilages 2-6.
• Receives IC nerves and depress the ribs.

Neurovascular Plane

• Runs between the internal and innermost intercostal muscles.
• Lies in the costal groove on the inferior border of the rib.
• Contains, from superior to inferior: IC vein, IC artery, and IC nerve (VAN).

Thoracic Spinal Nerves

• There are 12 pairs, each consisting of anterior and posterior rami.
  • 1st-11th anterior rami are IC nerves, the 12th is a subcostal nerve.
  • Posterior rami run posteriorly, supplying joints, deep muscles, and the skin of the thoracic region.

Intercostal Nerves

• Divided into 2 types: Typical and Atypical
  • Typical (3rd-6th)
  • Atypical (1st, 2nd, 7th-12th)

Typical Intercostal Nerve

• Runs between the endothoracic and parietal pleura.
• Course: Near the angle, between internal and innermost IC muscles.

Branches of Intercostal Nerves

• Collateral branch: Near the angle.
• Lateral cutaneous branch: At the midaxillary line (MAL).
• Anterior cutaneous branch: Near the sternum.

Atypical Intercostal Nerves

• The 1st nerve has 2 branches:
  • Large superior, the brachial plexus.
  • Small inferior, the 1st IC nerve.
• 1st & 2nd IC nerve: Course along the internal surface of the rib instead of the inferior border region
• 2nd IC nerve: Gives a large lateral cutaneous branch, supplying the axilla and forearm area.
• 7th-11th IC nerves: Cross the costal margin after giving the lateral cutaneous branch. -These continue to supply the skin of the abdominal wall and muscles, becoming thoracoabdominal nerves.

Arteries of the Thoracic Wall

• Mainly the thoracic aorta, along with the subclavian and axillary arteries.
• Posterior and Subcostal IC arteries.
• Internal and Supreme IC arteries.
• Superior and lateral thoracic arteries.
• Anterior IC artery, also known as internal thoracic artery.

Posterior Intercostal Artery

• Originates from the supreme IC artery (1st and 2nd)
• Costocervical branch of the subclavian artery.

Anterior Intercostal Artery

• From Internal Thoracic supply the anterior aspect of the upper 9 IC spaces

Internal Thoracic Artery

• Branch of the 1st part of the subclavian artery.
• Descends into the thorax posterior to the 1st rib and clavicle.
• Continues down lateral to the sternum and posterior to the upper 6 costal cartilages.
• Terminates in the sixth costal space, dividing into:
  • Superior epigastric artery
  • Musculophrenic artery