The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites (exoskeletal plates) are the metanotum (dorsal), the metasternum (ventral), and the metapleuron (lateral) on each side. The metathorax is the segment that bears the hindwings in most winged insects, though sometimes these may be reduced or modified, as in the flies (Diptera), in which they are reduced to form halteres, or flightless, as in beetles (Coleoptera), in which they may be completely absent even though forewings are still present.
The posterior segment of an insect's thorax is the metathorax and contains the third pair of legs. The key exoskeletal plates here are the metanotum, metasternum, and metapleuron on each side. In most winged insects, the metathorax supports the hindwings; however, in some species like flies (Diptera), these wings may be reduced or modified into halteres, while in beetles (Coleoptera), they might be entirely absent even if forewings are present.