Extremely uncommon.
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
lumbar vertebrae
"Lumbar" refers to the region of the back or spine made up of the lumbar vertebrae. The 1st lumbar vertebra is just under the 12th thoracic vertebra. The easiest way to find this is to find the first vertebral body not connected to a rib. This is L1 (1st lumbar vertebra). There are 5 lumbar vertebrae (L1 through L5). The 5th lumbar vertebra sits on top of the sacrum (where your spine connects with your pelvis).
Most likely it was the Lumper -- what's a 'Lumbar' potato?
The rib bone is also know as either the coastal ribs or floating ribs depending on the location of the rib bone.
Lumbar
A person typically has 24 ribs in their rib cage, arranged in 12 pairs, but variations can occur due to anatomical differences. Some individuals may have additional rib formations, such as a cervical rib or lumbar rib, leading to a total of 25 or more bones in the rib cage. These variations can be congenital and may not always cause health issues. It's essential for anyone with such variations to consult a healthcare professional for evaluation.
The bones in the torso are the rib cage, sternum, and vertebrae.
The common name for the costa bone is the rib cage. These are the curved arches of the bones that extend from the spine toward the sternum.
A rib
inflammation of the muscles in the lumbar region (lower back) it is a common symptom of flu.
A gorilla rib is a bone that is part of a gorilla's skeleton. It helps to protect the internal organs and provide structure and support for the gorilla's body. Gorilla ribs are large and strong, reflecting the physical power and size of these animals.