mesothorax
Noun
Meaning
The middle segment of the thorax in insects. See Illust. of Coleoptera.
Source: Webster's dictionaryExamples
The 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.
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.