Rib which has one end attached to the thoracic vertebra, but the other end is not attached to the sternum is called a false Rib. 8th-12th pair of parshukas Ribs are duplicate Ribs. Among them, the 8th, 9th and 10th vertebrae join together to form the costal arch. The ends of the 11th and 12th vertebrae are free or floating. These are called floating vertebrae. Between every two vertebrae are external and internal intercostal muscles. The space between the costal cartilages is called the intercostal space.