Xiphisternum

from The Collaborative International Dictionary of English v.0.48

Xiphisternum \Xiph"i*ster"num\, n.; pl. {Xiphisterna}. [NL., fr.
   Gr. xi`fos a sword + sternum.] (Anat.)
   (a) The posterior segment, or extremity, of the sternum; --
       sometimes called {metasternum}, {ensiform cartilage},
       {ensiform process}, or {xiphoid process}.
   (b) The xiphiplastron. -- {Xiph"i*ster"nal}a.
       [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Xiphiplastron \Xiph"i*plas"tron\, n.; pl. {Xiphiplastra}. [NL.,
   fr. Gr. xi`fos a sword + plastron.] (Anat.)
   The posterior, or fourth, lateral plate in the plastron of
   turtles; -- called also {xiphisternum}.
   [1913 Webster]