The thoracic cage protects the heart and lungs. It is composed of 12 pairs of ribs with their costal cartilages and the sternum. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The manubrium and body are joined at the sternal angle, which is also the site for attachment of the second ribs.
Ribs are flattened, curved bones and are numbered 1–12. Posteriorly, the head of the rib articulates with the costal facets located on the bodies of thoracic vertebrae and the rib tubercle articulates with the facet located on the vertebral transverse process. The angle of the ribs forms the most posterior portion of the thoracic cage. The costal groove in the inferior margin of each rib carries blood vessels and a nerve. Anteriorly, each rib ends in a costal cartilage. True ribs (1–7) attach directly to the sternum via their costal cartilage. The false ribs (8–12) either attach to the sternum indirectly or not at all. Ribs 8–10 have their costal cartilages attached to the cartilage of the next higher rib. The floating ribs (11–12) are short and do not attach to the sternum or to another rib.
angle of the rib
portion of rib with greatest curvature; together, the rib angles form the most posterior extent of the thoracic cage
body of the rib
shaft portion of a rib
clavicular notch
paired notches located on the superior-lateral sides of the sternal manubrium, for articulation with the clavicle
costal cartilage
hyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternum
costal groove
shallow groove along the inferior margin of a rib that provides passage for blood vessels and a nerve
false ribs
vertebrochondral ribs 8–12 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at all
floating ribs
vertebral ribs 11–12 that do not attach to the sternum or to the costal cartilage of another rib
head of the rib
posterior end of a rib that articulates with the bodies of thoracic vertebrae
jugular (suprasternal) notch
shallow notch located on superior surface of sternal manubrium
manubrium
expanded, superior portion of the sternum
neck of the rib
narrowed region of a rib, next to the rib head
sternal angle
junction line between manubrium and body of the sternum and the site for attachment of the second rib to the sternum
true ribs
vertebrosternal ribs 1–7 that attach via their costal cartilage directly to the sternum
tubercle of the rib
small bump on the posterior side of a rib for articulation with the transverse process of a thoracic vertebra
xiphoid process
small process that forms the inferior tip of the sternum
1. The sternum ________.
A) consists of only two parts, the manubrium and xiphoid process
B) has the sternal angle located between the manubrium and body
C) receives direct attachments from the costal cartilages of all 12 pairs of ribs
D) articulates directly with the thoracic vertebrae
B
2. The sternal angle is the ________.
A) junction between the body and xiphoid process
B) site for attachment of the clavicle
C) site for attachment of the floating ribs
D) junction between the manubrium and body
D
3. The tubercle of a rib ________.
A) is for articulation with the transverse process of a thoracic vertebra
B) is for articulation with the body of a thoracic vertebra
C) provides for passage of blood vessels and a nerve
D) is the area of greatest rib curvature
A
4. True ribs are ________.
A) ribs 8–12
B) attached via their costal cartilage to the next higher rib
C) made entirely of bone, and thus do not have a costal cartilage
D) attached via their costal cartilage directly to the sternum
D
1. Define the parts and functions of the thoracic cage.
The thoracic cage is formed by the 12 pairs of ribs with their costal cartilages and the sternum. The ribs are attached posteriorly to the 12 thoracic vertebrae and most are anchored anteriorly either directly or indirectly to the sternum. The thoracic cage functions to protect the heart and lungs.
2. Describe the parts of the sternum.
The sternum consists of the manubrium, body, and xiphoid process. The manubrium forms the expanded, superior end of the sternum. It has a jugular (suprasternal) notch, a pair of clavicular notches for articulation with the clavicles, and receives the costal cartilage of the first rib. The manubrium is joined to the body of the sternum at the sternal angle, which is also the site for attachment of the second rib costal cartilages. The body receives the costal cartilage attachments for ribs 3–7. The small xiphoid process forms the inferior tip of the sternum.
3. Discuss the parts of a typical rib.
A typical rib is a flattened, curved bone. The head of a rib is attached posteriorly to the costal facets of the thoracic vertebrae. The rib tubercle articulates with the transverse process of a thoracic vertebra. The angle is the area of greatest rib curvature and forms the largest portion of the thoracic cage. The body (shaft) of a rib extends anteriorly and terminates at the attachment to its costal cartilage. The shallow costal groove runs along the inferior margin of a rib and carries blood vessels and a nerve.
4. Define the classes of ribs.
Ribs are classified based on if and how their costal cartilages attach to the sternum. True (vertebrosternal) ribs are ribs 1–7. The costal cartilage for each of these attaches directly to the sternum. False (vertebrochondral) ribs, 8–12, are attached either indirectly or not at all to the sternum. Ribs 8–10 are attached indirectly to the sternum. For these ribs, the costal cartilage of each attaches to the cartilage of the next higher rib. The last false ribs (11–12) are also called floating (vertebral) ribs, because these ribs do not attach to the sternum at all. Instead, the ribs and their small costal cartilages terminate within the muscles of the lateral abdominal wall.