endothorax

from The Century Dictionary.

• noun In arthropods, as crustaceans and insects, the apodemal system of the thorax or the cephalothorax, formed by various processes and continuations of the dermal skeleton, and so constituting an interior framework of this part of the body, supporting and giving attachment to soft parts, as nerves and muscles.

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

• noun (Zoöl.) An internal process of the sternal plates in the thorax of insects.

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

• noun zoology An internal process of the sternal plates in the thorax of insects.