Humans typically have 24 ribs, consisting of 12 pairs. This number is generally consistent across individuals, regardless of sex.
Rib Structure and Function
The human rib cage, also known as the thoracic cage, is a bony structure that protects organs and assists in breathing. It is composed of 12 pairs of ribs, the sternum (breastbone), and the 12 thoracic vertebrae in the spine.
Ribs are categorized into three main types based on their attachment to the sternum. The first seven pairs are called “true ribs” because they connect directly to the sternum via their own costal cartilages. These cartilages allow for flexibility and movement during respiration.
The next three pairs, ribs 8 through 10, are known as “false ribs.” They do not attach directly to the sternum but instead connect to the cartilage of the rib above them. The final two pairs, ribs 11 and 12, are “floating ribs.” These only attach to the thoracic vertebrae at the back and have no anterior connection to the sternum or other ribs, allowing for greater mobility.
The function of the rib cage is to protect organs within the chest cavity, such as the heart and lungs, from external trauma. Beyond protection, the rib cage assists in respiration. Its flexible design allows it to expand and contract, which facilitates the expansion and deflation of the lungs as a person breathes.
Rib Count Variations
A common misconception suggests that men and women have a different number of ribs. This is not supported by scientific evidence; both sexes typically have 12 pairs of ribs. Anatomical variations in rib count occur in individuals regardless of gender.
Variations in rib numbers can occur, such as supernumerary ribs (extra ribs) or agenesis of ribs (fewer ribs). A notable example of an extra rib is a cervical rib, which originates from the seventh cervical vertebra in the neck. These extra ribs are relatively rare, with prevalence estimates ranging from 0.05% to 6.2% in the general population.
Most individuals with cervical ribs experience no symptoms and may be unaware of their presence. However, in some cases, a cervical rib can compress nerves or blood vessels in the neck and arm, leading to a condition called thoracic outlet syndrome (TOS). Symptoms of TOS can include pain, numbness, tingling, and weakness in the arm and hand, and sometimes coldness or discoloration of the hand.
Another less common variation is a lumbar rib, an extra rudimentary rib arising from the first lumbar vertebra. These are even rarer than cervical ribs. Lumbar ribs are often asymptomatic but can sometimes be associated with other spinal anomalies.