The Collaborative International Dictionary
hyposternum
Hypoplastron \Hy`po*plas"tron\, n.; pl. Hypoplastra. [Pref. hypo- + plastron.] (Anat.) The third lateral plate in the plastron of turtles; -- called also hyposternum.
Wiktionary
hyposternum
n. (context anatomy English) The hypoplastron.