Dictionary.net

• In insects, the third and last segment of the thorax-the second being called mesothorax.

1874 - Etymological and pronouncing dictionary of the English language
By Stormonth, James, Phelp, P. H.

• The posterior segment of the thorax of Insects.

1920 - A dictionary of scientific terms.
By Henderson, I. F.; Henderson, W. D.