How do ribs attach to the sternum in a horse?

In a horse and most mammals, the ribs attach to the sternum through costal cartilage. Costal cartilage is a flexible, fibrous tissue that connects the ends of the ribs to the sternum. The costal cartilages of the true ribs (ribs 1-7) are directly connected to the sternum, while the costal cartilages of the false ribs (ribs 8-10) are connected to each other and to the costal cartilage of the seventh rib. The floating ribs (ribs 11-13) are not connected to the sternum at all.

The costal cartilages allow for some movement of the ribs during respiration. When the muscles of inspiration contract, the ribs are pulled upward and outward, increasing the volume of the thoracic cavity and drawing air into the lungs. When the muscles of expiration relax, the ribs return to their resting position, decreasing the volume of the thoracic cavity and expelling air from the lungs.

The costal cartilages also provide support for the sternum and help to protect the heart, lungs, and other organs in the thoracic cavity.