The Collaborative International Dictionary of English v.0.48:

Costal \Cos"tal\ (k?s"tal), a. [Cf. F. costal. See Costa.]
   1. (Anat.) Pertaining to the ribs or the sides of the body;
      as, costal nerves.
      [1913 Webster]

   2. (Bot. & Zool.) Relating to a costa, or rib.
      [1913 Webster]

   Costal cartilage. See Cartilage, and Illust. of Thorax.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cartilage \Car"ti*lage\, n. [L. cartilago; cf. F. cartilage.]
   (Anat.)
   A translucent, elastic tissue; gristle.
   [1913 Webster]

   Note: Cartilage contains no vessels, and consists of a
         homogeneous, intercellular matrix, in which there are
         numerous minute cavities, or capsules, containing
         protoplasmic cells, the cartilage corpuscul. See Illust
         under Duplication.
         [1913 Webster]

   Articular cartilage, cartilage that lines the joints.

   Cartilage bone (Anat.), any bone formed by the ossification
      of cartilage.

   Costal cartilage, cartilage joining a rib with he sternum.
      See Illust. of Thorax.
      [1913 Webster]

WordNet (r) 3.0 (2006):

costal cartilage
    n 1: the cartilages that connect the sternum and the ends of the
         ribs; its elasticity allows the chest to move in
         respiration