The Collaborative International Dictionary of English v.0.48:

Pleurosteon \Pleu*ros"te*on\, n.; pl. L. Pleurostea, E.
   -ons. [NL., fr. Gr. ? a rib + ? a bone.] (Anat.)
   The antero-lateral piece which articulates the sternum of
   birds.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006):

ONS
       Object Numbering System (EPC)