2-24. THE RIBS
a. There are 12 pairs of ribs (figure 2-23). They are numbered from above
downward as the first, second, third, and so forth., and as the right or the left. The 1st,
11th, and 12th ribs articulate posteriorly with the body of the corresponding vertebrae,
while the remaining ribs articulate with the corresponding vertebrae as well as with the
vertebrae immediately above. The first seven pairs are the true (sternal) ribs; their
anterior extremities articulate with the sternum by means of the costal cartilages. The
remaining five pairs are the false (asternal) ribs; they are not connected directly to the
sternum. The 8th, 9th, and 10th ribs have their cartilages attached to the cartilage of
the rib above and are called the vertebrochondral ribs. The 11th and 12th ribs are free
at their anterior extremities and are floating (vertebral) ribs.
b. A typical rib (figure 2-25) possesses the following common characteristics.
(1) A vertebral extremity that presents for examination a head that
articulates with the superior demifacet of the corresponding vertebra and the inferior
demifacet of the vertebra above a short constricted part called the neck, and a tubercle,
consisting of a medial articular portion and a lateral nonarticular portion. The articular
portion is for articulation with the costal facet on the transverse process of the
corresponding thoracic vertebra. The nonarticular portion is for the attachment of
(2) A body or shaft, the long, flattened, curved part of the rib is marked by
an angle and a costal groove.
(3) An oval pit into which the costal cartilage is received marks a flattened
Figure 2-25. A typical rib.