The first rib is occasionally absent. A case of incomplete development of the third and fourth ribs, and the absence of ribs eight, nine, and ten has been reported. In another subject, ribs two, three, four, and five were absent. Differences in length are important considerations in the surgical approach to the kidney. The twelfth rib may be absent on one side and shortened on the other side.
Asymmetric ribs are common.
A bicipital rib is seen in relation to the first thoracic rib. It appears to be the result of the fusion of two ribs, either of a cervical and first thoracic or of the first two thoracic ribs. Fusion of the first two ribs is common. The first rib may be ossified at its extremities but fibrous between. The scapula may be fixed to the first rib by a short costocoracoid ligament.