Hypocleidium \Hy`po*clei"di*um\, n.; pl. L. {Hypocleida}, E.
{Hypocleidiums}. [NL., fr. Gr. ? under + ? a little key.]
(Anat.)
A median process on the furculum, or merrythought, of many
birds, where it is connected with the sternum.
[1913 Webster]