The costal cartilage are segments of cartilage that connect the sternum to the ribs and help to extend the ribs into a forward motion. This cartilage also contributes to elasticity within the walls of the thorax, allowing the chest to expand during respiration. There are twelve costal cartilage sections. Each has two cartilages, extremities, and borders. Seven pairs of the costal cartilage are connected to the sternum. Two of the costal cartilage sections are pointed, ending in the walls of the abdomen. Three pairs of costal cartilage are articulated (connected) with the preceding ribs. The anterior (front) surfaces are convex, while the posterior (rear) surfaces are concave. The borders are superior and inferior in nature. The superior section is concave, while the inferior is convex. The eleventh and twelfth costal cartilage segments are pointed and are free of attachments. Once a person reaches age 65 and beyond, their costal cartilage becomes prone to superficial ossification, or hardening into a bony substance.