entoplastron

from The Century Dictionary.

• noun The single median and anterior one of the nine pieces of which the plastron usually consists in chelonians or turtles and tortoises: so named by Huxley to avoid the use of the more frequent name entosternum, as the plastron is not now supposed to contain any sternal elements. See epiplastron, and cuts under carapace, Chelonia (second cut), and plastron.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Anat.) The median plate of the plastron of turtles; -- called also entosternum.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy The median plate of the plastron of turtles.