costole

Costole are the bones that form the rib cage. In humans there are 24 costole, arranged as 12 pairs on either side of the thorax. Each costole links posteriorly with a thoracic vertebra and anteriorly with the sternum or adjacent costal cartilage.

Anatomically, a typical costole consists of a curved shaft with a head that articulates with the vertebral bodies and a tubercle that articulates with the transverse process. The anterior end is connected to costal cartilage, which in turn attaches to the sternum, forming the thoracic cage.

Classification and articulation: True ribs 1–7 have direct costal cartilage attachments to the sternum; false ribs 8–10 connect indirectly via the cartilage of the rib above; floating ribs 11–12 have no anterior attachment. The thoracic cage also houses intercostal muscles and neurovascular bundles between ribs.

Function: The costole protect thoracic organs such as the heart and lungs, and participate in respiration by increasing and decreasing thoracic volume during inhalation and exhalation. They also provide attachment sites for muscles of respiration, posture, and upper limb movement.

Development and variation: Costole develop from mesoderm and ossify during late fetal life and early adulthood. Variation includes cervical ribs or anomalous costal attachments. Costal cartilage is hyaline cartilage that can ossify with age, and fractures of a costole are common injuries.