Ribs

The ribs (costae), in vertebrate anatomy, are the long curved bones which form the rib cage.

In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They protect the lungs, heart, and other internal organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.

The ribs are composed by:

• A dorsal bony (osseous) part (termed in latin the os costale, and not costae) subdivised in head, neck, tubercle and the body (shaft).

• A ventral cartilagenous part termed the costal cartilage, connected to the rib at the costochondral junction and that articulates by its sternal extremity with the sternum (forming the sternocostal joints).

The true ribs (sternal ribs) are directly connected to the sternum. The false ribs (asternal ribs) are indirectly connected to the sternum by uniting with the cartilage of the last sternal rib, forming the costal arch. The floating ribs are the most caudal ribs, whose cartilage ends free in the musculature without attachment to an adjacent cartilage.

The number of ribs differs between species:

• Carnivores:12-14 (9 sternal, 4 asternal)

  • Dogs: 13 (9 sternal, 4 asternal)

  • Cats: 13 (9 sternal, 4 asternal)

• Pigs: 13-16 (7 sternal, 7-8 asternal)

• Ruminants: 13 (8 sternal, 5 asternal)

• Horse 18 (8 sternal, 10 asternal)