entoplastron

Coined by Thomas Henry Huxley in 1872 as ento- +‎ plastron. Superseded the earlier entosternum, a nominalised form of the French adjective entosternal, coined by Étienne Geoffroy Saint-Hilaire in 1818. The prefix is from Ancient Greek ἐντός (entós, “inner”), in reference to its position as the unpaired bone at the centre of the plastron.