The Collaborative International Dictionary of English v.0.48:

Omosternum \O`mo*ster"num\, n. [Omo- + sternum.] (Anat.)
   (a) The anterior element of the sternum which projects
       forward from between the clavicles in many batrachians
       and is usually tipped with cartilage.
   (b) In many mammals, an interarticular cartilage, or bone,
       between the sternum and the clavicle.
       [1913 Webster]