Noun
The middle segment of the thorax in insects. See Illust. of Coleoptera.
Source: Webster's dictionaryThe mesothorax and metathorax are fused into a rigid, box-like structure with internal bracing, and provides a robust attachment for the powerful wing muscles inside it. citation The thorax bears two pairs of wings and three pairs of legs. Source: Internet
The mesothorax is designed to have more powerful muscles to propel the moth or butterfly through the air, with the wing of this segment (fore wing) having a stronger vein structure. Source: Internet