Thorax - Ribs

Question 1

Boney features of typical ribs:

Answer 1

Posteriorly :

Head - has 2 facets separated by crest of head.

Neck- constricted portion, connects head to body at level of the tubercle.

Tubercle -
• junction between neck and body.
• medically has a smooth articular surface which articulates with the transverse process of vertebrae.
• laterally has a rough non-articular surface which provides attachment to the costotransverse ligament.

Costal angle:

• part of rib where is Turns anterolaterally
• demarcates lateral limit of attachment of deep back muscles to rib.

Subcostal groove:

• located on the concave internal surface of the body of the rib.
• parallel to the inferior border.
• provides protection to intercostal nerve and vessels.

Question 2

Which ribs are typical and which are atypical?

Answer 2

Typical - 3rd to 9th rib

Atypical - 1,2,10,11,12 ribs

Question 3

Boney features of atypical Ribs.

Rib : 1

Answer 3

• head only has one facet for articulation with T1 vertebrae.
• shortest rib
• broadest rib
• sharpest of the 7 true ribs
• has 2 transversely directed grooves crossing the superior surface (for subclavian vessels)
• the grooves are separated by a scalene tubercle.
• the scalene tubercle gives attachment to the scalene muscle.

Question 4

Boney features of Atypical Ribs :

2nd Rib

Answer 4

• Thinner, less curved
• twice as long as the first rib.
• has 2 facets on the head posteriorly to articulate with T1 and T2 vertebrae.
• it’s main Atypical feature is the roughness on it’s superior surface.
• it has a serratus tubercle on it’s superior surface which gives attachment to the serratus anterior muscle.

Question 5

Boney features of an atypical rib:

10th Rib

Answer 5

• has all the features of a typical bone
• it differentiates form a typical bone because : • it is shorter than a typical bone and it only has one facet on its head to articulate with the 10th thoracic vertebrae.

Question 6

Feature of an atypical bone :

11th Rib

Answer 6

• poorly marked costal angle and subcostal groove.
• no neck or tubercle.
• shorter
• only one facet located on the head for articulation with a thoracic vertebrae.

Question 7

Boney features of atypical ribs:

12th rib

Answer 7

• no costal angle or groove
• no neck or tubercle
• shorter
• only one facet on head for articulation with a thoracic vertebrae.

Question 8

External intercostal muscles (attachments)

Answer 8

• The muscle fibers are running downwards.
• The superior border of the rib below.
• The inferior border of the rib above.
• The exterior intercostal muscle: replaces the the anterior muscle fibers.

Question 9

Internal intercostal muscle

Answer 9

• The muscle fibers are moving upwards.
• Origin: inner lip of the superior border of rib below.
• insertion: external lip of subcostal groove on the interior border of rib above.
• posteriorly, medial to costal angle muscle fibers are replaced by internal intercostal membrane.

Question 10

Innermost intercostal muscle

Answer 10

• Deep to the internal intercostal muscles.
• separates internal intercostal muscle and innermost intercostal muscle.
• inner lip of the superior border of rib below.
• external lip of subcostal groove on the inferior border of the rib above.

Question 11

Scalene Anterior

Answer 11

Scalene tubercle on first rib

Question 12

Subcostal

Answer 12

• origin : internal surface of lower ribs near their costal angle.
• superior borders of 2nd or 3rd ribs below.

Question 13

Serratus anterior

Answer 13

• Serratus tubercle on the 2nd rib -lateral borders of 1-8 th ribs

Question 14

Scalene Media’s

Answer 14

Subcostal groove on the posterior side of the first rib.

Question 15

Scalene posterior

Answer 15

Lateral end of posterior surface of 2nd rib.