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The ribs begin to develop in the mesoderm during the sixth week of prenatal life:
- develop by intracartilaginous ossification
- if a rib is destined to have an angle, this is the primary centre of ossification at 8 weeks
- otherwise, ossification commences from the midshaft distally
- the secondary centres of ossification are the head and tubercle which appear in late puberty
- ossification is completed by 22-26 years of age
- the costal cartilage represents unossified rib
Anomalies can occur in the number and form of ribs. Otherwise physically healthy people can possess between 11 and 14 pairs of ribs. Infrequently, both lumbar and cervical accessory ribs occur due to the overdevelopment of the costal process of the transverse processes of L1 and C7 respectively.
Last reviewed 01/2018