These are the laterally directed notches that form synovial joints with the first seven costal cartilages of the true ribs. The first notch forms on the wide lateral process of the manubrium. The second notch sits at the junction of the manubrium and the body. Four complete notches form on the lateral margin of the body at the fusion lines of adjacent sternebrae. A final costal notch occurs at the junction of the xiphoid process and body, each element contributing a demifacet.

Costal comes from the Latin word costa meaning rib. The term notch refers to an indentation in the margin of a bone. The Latin equivalent for this term is incisure.