There are l2 pairs of ribs on the skeleton.

Look at the posterior side of the thorax: All articulate with the thoracic vertebrae.

Lets have a look at the anterior side of the thorax:

The first 7 pairs (= true ribs) are joined directly to the sternum through costal cartilages.

The costal cartilages of ribs 8, 9 and l0 (= false ribs) are attached to the costal cartilage of the rib immediately above.

Ribs ll and l2 (= floating ribs) are not attached anteriorly.

Note the progressive change in shape of the ribs.

Examine an individual rib.

A rib is made of:

1- a head
it is a projection at the posterior end of the rib and it joints with the thoracic vertebrae,

2- a neck
it is a constricted portion between the head and the shaft. It contains a knoblike structure (= the tubercle) on its posterior surface near its junction with the shaft,

3- a shaft (= body)
it makes most of the rib.

Identify the sternal and vertebral ends.
Most ribs have a double articulation with the vertebral column. Facets on the head of the rib articulate with the bodies of thoracic vertebrae. A third facet is present on the tubercle of most ribs. This articulates with the transverse process of the vertebra.