<P> The phrase floating rib (Latin: costae fluitantes) refers to the two lowermost, the eleventh and twelfth, rib pairs; so - called because they are attached only to the vertebrae--and not to the sternum or cartilage of the sternum . These ribs are relatively small and delicate, and include a cartilaginous tip . </P> <P> The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, arteries, and veins . </P> <P> Each rib consists of a head, neck, and a shaft, and they are numbered from top to bottom . The head of a rib is the end part closest to the spine with which it articulates . It is marked by a kidney - shaped articular surface which is divided by a horizontal crest into two facets . The superior facet is smaller and articulates with the vertebra above, and the inferior facet articulates with the vertebra of the same number . The transverse process of a thoracic vertebra also articulates with the rib of the same number . The crest gives attachment to the intra-articular ligament . All ribs are attached posteriorly to the thoracic vertebrae . </P> <P> The neck of the rib is the flattened part that extends laterally from the head . The neck is about 3 cm long, and is placed in front of the transverse process of the lower of the two vertebrae with which the head articulates . Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck . </P>

Where does the head of the rib attach