"Costal cartilages 1-7 articulate with the sternum at sternocostal joints, and costal cartilages 8-10 are attached via small interchondral synovial joints forming the costal margin."
"There are ten costal cartilages bilaterally, one for each of the corresponding 1st to 10th ribs, and each of the first seven ribs forms one of the seven costochondral joints."