What is gorilla rib in some humans?

The term "Gorilla rib" is used to describe a Lumbar rib. Most humans only have ribs bilaterally attached to their 12 thoracic vertebra but a number of variations exist with cervical ribs, lumbar ribs and even so called sacral ribs. Approximately 8% of humans have a extra rib attached to their lumbar vertebra which also occurs in some types of gorillas