Skeleton of the Thorax : Sternum, Ribs

October 7, 2012 | By | Reply More

Skeleton of the Thorax : Sternum, Ribs

■ Is a fl at bone and consists of the manubrium, the body, and the xiphoid process.
■ Is relatively shorter and thinner in the female, and its body is more than twice as long as the manubrium in the male but is usually less in the female.
1. Manubrium
■ Has a superior margin, the jugular notch, which can be readily palpated at the root of the neck.
■ Has a clavicular notch on each side for articulation with the clavicle.
■ Also articulates with the cartilage of the fi rst rib, the upper half of the second rib, and the body of the sternum at the manubriosternal joint, or sternal angle.
2. Sternal Angle (Angle of Louis)
■ Is the junction between the manubrium and the body of the sternum.
■ Is located at the level where:
■ The second ribs articulate with the sternum.
■ The aortic arch begins and ends.
■ The trachea bifurcates into the right and left bronchi at the carina.

■ The inferior border of the superior mediastinum is demarcated.
■ A transverse plane can pass through the intervertebral disk between T4 and T5.

3. Body of the Sternum
■ Articulates with the second to seventh costal cartilages.
■ Also articulates with the xiphoid process at the xiphisternal joint, which is at level with the ninth thoracic vertebra.
4. Xiphoid Process
■ Is a fl at, cartilaginous process at birth that ossifi es slowly from the central core and unites with the body of the sternum after middle age.
■ Lies at the level of T10 vertebra, and the xiphisternal joint lies at the level of the T9 vertebral body, which marks the lower limit of the thoracic cavity in front, the upper surface of the liver, diaphragm, and lower border of the heart.
■ Can be palpated in the epigastrium and is attached via its pointed caudal end to the linea alba.

■ Consist of 12 pairs of bones that form the main part of the thoracic cage, extending from the vertebrae to or toward the sternum.
■ Increase the anteroposterior and transverse diameters of the thorax by their movements.

■ Typical ribs are ribs 3 through 9, each of which has a head, neck, tubercle, and body (shaft).
■ The head articulates with the corresponding vertebral bodies and intervertebral disks and supra-adjacent vertebral bodies.
■ The body (shaft) is thin and fl at and turns sharply anteriorly at the angle and has a costal groove that follows the inferior and internal surface of a rib and lodges the intercostal vessels and nerves.
■ The tubercle articulates with the transverse processes of the corresponding vertebrae, with the exception of ribs 11 and 12.
a. True Ribs
■ Are the first seven ribs (ribs 1 to 7), which are attached to the sternum by their costal cartilages.
b. False Ribs
■ Are the lower fi ve ribs (ribs 8 to 12); ribs 8 to 10 are connected to the costal cartilages immediately above, and thus the 7th to 10th costal cartilages form the anterior costal arch or costal margin.
c. Floating Ribs
■ Are the last two ribs (ribs 11 and 12), which are connected only to the vertebrae.

First Rib
■ Is the broadest and shortest of the true ribs.
■ Has a single articular facet on its head, which articulates with the fi rst thoracic vertebra.
■ Has a scalene tubercle for the insertion of the anterior scalene muscle and two grooves for the subclavian artery and vein.

Second Rib
■ Has two articular facets on its head, which articulate with the bodies of the fi rst and second thoracic vertebrae.
■ Is about twice as long as the fi rst rib.
Tenth Rib
■ Has a single articular facet on its head, which articulates with the 10th thoracic vertebra.
Eleventh and Twelfth Ribs
■ Have a single articular facet on their heads.
■ Have no neck or tubercle.

Category: Anatomy

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