A cervical rib in humans is an extra rib which comes off of the seventh cervical vertebra. Sometimes known as “neck ribs”, their presence is a congenital abnormality located above the normal first rib, which comes off the first thoracic vertebra. A cervical rib is present in only about 1 in 500 (0.2%) people. In even rarer cases, an individual may have two cervical ribs. The presence of a cervical rib can sometimes interfere with nearby blood vessels and/or nerves, resulting in neck pain or numbness in the arm known as thoracic outlet syndrome.
National Health Service, August 2012