The Collaborative International Dictionary of English v.0.48:

Subcostal \Sub*cos"tal\, a. (Anat. & Zool.)
   Situated below the costas, or ribs; as, the subcostal
   muscles.
   [1913 Webster]

   Note: The subcostal muscles are distinct from, and within,
         the intercostal.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Subcostal \Sub*cos"tal\, n.
   1. (Anat.) A subcostal muscle.
      [1913 Webster]

   2. (Zool.) One of the principal nervures of the wings of an
      insect. It is situated next beneath or behind the costal.
      See Nervure.
      [1913 Webster]