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The mesothorax is the middle of the three segments in the thorax
Thorax

The thorax is a division of an animal's body that lies between the head and the abdomen.In mammals, the thorax is the region of the body formed by the sternum, the thoracic vertebrae and the ribs....
 of an insect
Insect

Insects are the biggest class of arthropods and the only ones with wings. They are the most diverse group of animals on the planet. They are most diverse at the equator and their diversity declines toward the poles....
, and bears the second pair of legs. Its principal sclerites (exoskeletal plates) are the mesonotum (dorsal
Dorsum (biology)

In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright....
), the mesosternum (ventral), and the mesopleuron (lateral
Lateral

Lateral may prefer a :*Lateral, an anatomical direction - see Human anatomical terms#Anatomical directions*Lateral pass, type of pass in American and Canadian football...
) on each side. The mesothorax is the segment that bears the forewings in all winged insects, though sometimes these may be reduced or modified, as in beetle
Beetle

Beetles are the group of insects with the largest number of known species. They are placed in the order Coleoptera , which contains more described species than in any other order in the animal, constituting about 25% of all known life-forms....
s (Coleoptera) or Dermaptera, in which they are sclerotized to form the elytra ("wing covers"), and the Strepsiptera
Strepsiptera

The Strepsiptera are an order of insects with nine families making up about 600 species. The early stage larvae and the short-lived adult males are free-living but most of their life is spent as endoparasites in other insects such as bees, wasps, leafhoppers, silverfish, and cockroaches....
, in which they are reduced to form halteres
Halteres

Halteres are small knobbed structures found as a pair in some two-winged insects. They are flapped rapidly and function as accelerometers to help the insect maintain stability in flight, analogous to an aircraft's attitude indicator....
.






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The mesothorax is the middle of the three segments in the thorax
Thorax

The thorax is a division of an animal's body that lies between the head and the abdomen.In mammals, the thorax is the region of the body formed by the sternum, the thoracic vertebrae and the ribs....
 of an insect
Insect

Insects are the biggest class of arthropods and the only ones with wings. They are the most diverse group of animals on the planet. They are most diverse at the equator and their diversity declines toward the poles....
, and bears the second pair of legs. Its principal sclerites (exoskeletal plates) are the mesonotum (dorsal
Dorsum (biology)

In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright....
), the mesosternum (ventral), and the mesopleuron (lateral
Lateral

Lateral may prefer a :*Lateral, an anatomical direction - see Human anatomical terms#Anatomical directions*Lateral pass, type of pass in American and Canadian football...
) on each side. The mesothorax is the segment that bears the forewings in all winged insects, though sometimes these may be reduced or modified, as in beetle
Beetle

Beetles are the group of insects with the largest number of known species. They are placed in the order Coleoptera , which contains more described species than in any other order in the animal, constituting about 25% of all known life-forms....
s (Coleoptera) or Dermaptera, in which they are sclerotized to form the elytra ("wing covers"), and the Strepsiptera
Strepsiptera

The Strepsiptera are an order of insects with nine families making up about 600 species. The early stage larvae and the short-lived adult males are free-living but most of their life is spent as endoparasites in other insects such as bees, wasps, leafhoppers, silverfish, and cockroaches....
, in which they are reduced to form halteres
Halteres

Halteres are small knobbed structures found as a pair in some two-winged insects. They are flapped rapidly and function as accelerometers to help the insect maintain stability in flight, analogous to an aircraft's attitude indicator....
. All adult insects possess legs on the mesothorax. In some groups of insects, the mesonotum is hypertrophied, such as in Diptera, Hymenoptera
Hymenoptera

Hymenoptera is one of the larger order s of insects, comprising the sawfly, wasps, bees, and ants. The name refers to the membranous wings of the insects, and is derived from the Ancient Greek language wikt:???? : membrane and wikt:pte??? : wing....
, and Lepidoptera
Lepidoptera

Lepidoptera is an order of insect that includes moths and butterfly. It is one of the most speciose orders in the class Insecta, encompassing moths and the three superfamilies of butterfly, skipper , and Hedylidae....
), in which the anterior portion of the mesonotum (called the mesoscutum
Scute

A scute or scutum is a chitinous, or bony external plate or scale, as on the shell of a turtle, the skin of crocodiles, or the feet of some birds....
, or simply "scutum") forms most of the dorsal surface of the thorax. In these orders, there is also typically a small sclerite attached to the mesonotum that covers the wing base, called the tegula
Tegula (anatomy)

A tegula is a small sclerite situated above the base of the costal vein in the wings of various insects such as Lepidoptera, Hymenoptera, Diptera, and Homoptera, and attached to the antero-lateral portion of the mesonotum....
. In one group of insects, the Hemiptera
Hemiptera

Hemiptera is an order of insects, comprising around 80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others. They range in size from 1 mm to around 15 cm, and share a common arrangement of sucking mouthparts ....
, the dorsal surface of the thorax is typically formed primarily of the prothorax, but also in part by the enlarged posterior portion of the mesonotum, called the scutellum
Scutellum

The scutellum is the posterior portion of either the mesonotum or the metanotum of an insect thorax; however, it is used almost exclusively in the former context, as the metanotum is rather reduced in most insect groups....
; in the Coleoptera, the scutellum may or may not be visible, usually as a small triangular plate between the elytral bases, thus similar in position to the Hemiptera
Hemiptera

Hemiptera is an order of insects, comprising around 80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others. They range in size from 1 mm to around 15 cm, and share a common arrangement of sucking mouthparts ....
n scutellum. In Diptera and Hymenoptera
Hymenoptera

Hymenoptera is one of the larger order s of insects, comprising the sawfly, wasps, bees, and ants. The name refers to the membranous wings of the insects, and is derived from the Ancient Greek language wikt:???? : membrane and wikt:pte??? : wing....
 the mesothoracic scutellum is also distinct, but much smaller than the mesoscutum.